METALLURGY 


A  CONDENSED  TREATISE 


FOR  THE  USE  OF 


College  Students  and  Any  Desiring  a 

General  Knowledge  of  the 

Subject 


BY 


HENRY    WYSOR,    B.S. 
t « 

ASSISTANT  PROFESSOR  OF  ANALYTICAL  CHEMISTRY  AND 
METALLURGY  IN  LAFAYETTE  COLLEGE 


EASTON,  PA.: 
THE  CHEMICAL  PUBLISHING  CO. 

^ 

THE 

TY 

J     LONDON,  ENGLAND : 
^X 

WILLIAMS  &  NORGATE 

14  HENRIETTA  STREET,  COVENT  GARDEN,  W.  C. 


COPYRIGHT,  1908,  BY  EDWARD  HART. 


PREFACE 

I  offer  this  book  as  a  guide  to  the  science  of  Metallurgy. 
The  general  scheme  is  the  setting  forth  of  the  principles  in- 
volved in  the  subject;  the  description  of  processes  or  groups 
of  processes,  and  such  reasoning  as  is  calculated  to  show  the 
applications  of  natural  law  in  the  operations  considered.  The 
ideal  is  the  embodiment  of  the  history,  practice  and  philosophy 
of  metallurgy  in  a  single  volume,  admitting  only  such  matter 
as  is  essential  to  the  student. 

So  composite  a  subject  as  metallurgy  is  not  easily  presented 
in  a  short  course  of  lectures,  nor  can  it  be  elaborated  in  a 
treatise  of  this  size.  Exhaustive  literature,  however,  is  not 
lacking.  From  the  classic  works  of  Percy  to  the  standard  texts 
and  journals  of  the  present  time,  and  with  the  numerous  transla- 
tions, there  is  ample  reference  literature  in  the  English  language. 
I  have  felt  from  my  own  experience,  and  from  the  opinions 
of  others  engaged  in  teaching  and  in  practical  work,  that  a 
condensed  manual  is  needed  in  the  colleges  of  this  country.  It 
is  therefore  expected  that  this  book  will  be  of  assistance  to  stu- 
dents, teachers  and  others  who  need  some  general  information 
in  different  branches  of  metallurgy. 

I  take  pleasure  in  acknowledging  my  indebtedness  to  co- 
operators.  Among  these  are  the  several  manufacturers  of 
metallurgical  appliances,  who  have  furnished  the  excellent  plates 
and  drawings  to  which  their  names  are  appended. 

I  extend  my  hearty  thanks  to  personal  friends  for  their  as- 
sistance, and  especially  to  my  teacher,  Prof.  R.  C.  Price,  whose 
suggestions  were  invaluable  and  whose  interest  is  highly  ap- 
preciated. 

H.  W. 

Easton,  Pa.,  May,  1908. 


177755 


INTRODUCTION 

The  science  of  Metallurgy  treats  of  the  properties  of  the  metals 
and  of  the  processes  by  which  they  are  prepared  from  their  ores. 
The  science  embraces  a  study  of  the  ores,  fuels  and  all  the  mate- 
rials used  in  metallurgical  industries,  together  with  the  structures 
and  machinery  employed. 

Metallurgical  processes  are  essentially  chemical.  The  metals 
generally  occur  in  such  stable  combinations  as  to  require  reacting 
substances  and  often  the  powerful  agency  of  heat  to  bring  about 
their  separation  and  purification.  As  viewed  in  this  light,  metal- 
lurgy might  be  classed  as  a  branch  of  industrial  chemistry.  The 
industry  has,  however,  grown  to  such  enormous  proportions,  and 
is  so  closely  linked  with  other  branches  of  engineering,  as  to  war- 
rant its  being  studied  as  a  separate  branch. 

An  understanding  of  the  physical  and  chemical  properties  of 
the  metals,  fuels  and  refractory  materials  is  essential  to  the  metal- 
lurgist, and  he  must  also  familiarize  himself  with  machinery,  which 
has  come  to  play  so  important  a  part  in  modern  practice.  With 
these  facts  in  view,  the  principles  upon  which  metallurgical  opera- 
tions in  general  are  conducted,  are  laid  down  in  the  opening 
chapters  of  this  treatise,  and  a  special  study  is  made  of  the  fuels 
and  refractory  earths,  the  construction  of  furnaces  and  combus- 
tion. It  is  the  aim  throughout  this  book  to  show  the  application 
of  scientific  principles  in  winning  the  useful  metals,  and  while 
much  of  the  matter  is  necessarily  descriptive,  it  is  to  the  end 
stated  that  the  student's  attention  is  especially  called. 


CONTENTS 


INTRODUCTION 


CHAPTER  I 
Physical  Properties  of  the  Metals 

Fracture i 

Tenacity 2 

Elasticity 2 

Testing  machines 3 

Toughness 5 

Malleability 5 

Ductility 5 

Wire  drawing 5 

Flow   6 

Brittleness 6 

Drop  testing 6 

Hardness 6 

Fusibility  and  volatility 6 

Diffusion    7 

Welding 7 

Occlusion '. 7 

Conductivity 8 

Magnetism 8 

Density 8 

Tables  of  Tenacity,  Malleability  and  Ductility 8 

Table  of  Physical  Constants    9 

CHAPTER  II 
Refractory  Materials  and  Fluxes 

Classification 10 

Acid  Materials 

Silica 10 

Sand II 

Silica  brick n 

Clay , ii 

Testing  fire-clay 12 

Canister 13 


VI  CONTENTS 

Basic  Materials 

Magnesia !  3 

Lime T3 

Dolomite    H 

Bauxite 1 4 

Neutral  Materials 

Graphite 14 

Chromite • •  •  •  •  J4 

The  Fluxes 

CHAPTER  III 
Theory  of  Combustion  and  Thermal  Measurements 

Offices  of  fuels 16 

Calorific  power  by  experiment 17 

Calorific  power  by  calculation 19 

Calorific  intensity 19 

Pyrometry  19 

Fusion  point  pyrometer  20 

Metal  expansion  pyrometer 20 

Specific  heat  pyrometer 20 

Heat  conduction  pyrometer 20 

Air  pyrometer 20 

Optical  pyrometer 21 

Electric  resistance  pyrometer 21 

Thermo-electric  pyrometer 21 

Bristol  pyrometer 21 

Table  of  calorific  values 23 

CHAPTER  IV 

Classification  and  Description  of  the  Fuels— The  Natural  Fuels 

Wood • 24 

Peat 24 

Lignite 25 

Coal 26 

Coals  classified - 27 

Bituminous  coal 27 

Class  i.     Cannel  coals 27 

Class  2.     Long  flame— caking  coals 27 

Class  3.     Short  flame— coking  coals 28 

Anthracite 28 

Natural  gas • • 28 


CONTENTS  Vll 

CHAPTER  V 
The  Prepared  Fuels 

Charcoal ^i 

Coke 32 

The  beehive  oven 33 

Ovens  excluding  air  and  burning  the  by-products 35 

Ovens  excluding  air  and  recovering  the  by-products 35 

Otto-Hoffman  oven 36 

Coke  quenching  machines 38 

Desulphurization  of  coke 38 

Theoretical  considerations — status  of  coke  manufacture 38 

Producer  gas 40 

Water  gas 44 

Typical  analyses  of  fuels 45 

CHAPTER  VI 

Ore  Dressing 

Ores 46 

Ore  deposits 46 

1.  Ore  dressing 47 

2.  Extraction  of  the  metal 47 

3.  Refining 47 

4.  Mechanical  treatment 48 

Weathering 48 

Hand  picking 48 

Breaking 49 

Pulverizing 51 

Stamp  mill 51 

Chilian  mill 53 

Huntington  mill 53 

Screening 53 

Washing 54 

J'g 54 

Frue  vanner 55 

Magnetic   separating 56 

Wetherill  separator 57 

Calcining  and  roasting 57 

Mixing  ores 57 

CHAPTER  VII 
Furnaces 

1.  Furnaces  in  which  the  fuel  and  substance  treated  are  in  contact  ....  60 

2.  Furnaces  in  which  the  substance  treated  is  in  contact  with  the  flame 

and  products  of  combustion,  but  not  in  contact  with  the  fuel 62 


Vlll  CONTENTS 

3.  Furnaces  in  which  the  substance  treated  is  not  in  contact  with  either 

the  fuel  or  the  products  of  combustion 62 

4.  Electric  furnaces 63 

Regenerative  firing 63 

Retrospective 63 

CHAPTER  VIII 

Iron— Ores  and  Properties 

History 65 

Ores 

Oxides '.  . .  65 

Hematite 65 

Magnetite    66 

Carbonates 66 

Sulphides 67 

Some  impurities  in  iron  ores .   67 

Dressing  iron  ores 68 

Properties 

Pure  iron 68 

Effects  of  other  elements  on  iron 69 

Chemical  properties 76 

CHAPTER    IX 
Iron  Smelting— Chemistry  of  the  Blast  Furnace  Process 

Pig  iron 77 

Preliminary  description  of  the  blast  furnace  process 77 

Chemical  changes  in  the  blast  furnace 79 

Blast  furnace  slag 83 

Wall  accretions • 84 

Blast  furnace  gas 85 

CHAPTER  X 
Iron  Smelting — The  Blast  Furnace  Plant  and  Process 

Description  of  the  plant 86 

The  stack 87 

Tuyeres 89 

Charging  apparatus 90 

Dust  catchers 9I 

Stoves 93 

Blowing  engines 95 

Blowing  in 97 

Burdening 9g 

Fuels  and  fluxes Ioo 

Management  of  the  blast IOI 


CONTENTS  ix 

Dry  blast  apparatus IO5 

Casting IO5 

Disposal  of  slag 107 

Disposal  of  flue  dust roy 

Thermal  requirements  and  economy  of  fuel 108 

CHAPTER  XI 
Cast  Iron 

Properties  and  uses no 

Grading m 

Iron  Founding 

Melting 1 13 

Mixing II5 

Casting TI6 

Malleable  castings j  jg 

Testing  cast  iron !  I9 

CHAPTER    XII 
Wrought  Iron 

Historical 121 

Properties 1 23 

Manufacture  of  Wrought  Iron 

The  puddling  process 124 

Dry  puddling 125 

Pig  boiling  process 126 

Modifications  of  the  puddling  process 1 29 

Mechanical  puddling 130 

CHAPTER  XIII 

Steel— The  Cementation  and  Crucible  Processes 
Definition 131 

The  Cementation  Process 

The  furnace 131 

The  process 132 

The  Crucible  Process 

Crucibles    134 

The  melting  furnace 135 

The  process 135 

CHAPTER  XIV 

Steel — The  Bessemer  Process 

Acid 

History 137 

The  iron  mixer 138 


X  CONTENTS 

The  converter 138 

The  process 141 

Theory  of  the  process 143 

Basic 

The  process 144 

CHAPTER  XV 

Steel— The  Open  Hearth  Process 

History 145 

Acid 

The  process 147 

Basic 

Details 150 

Chemistry  of  the  Open  Hearth  Process 

Silicon 152 

Carbon : 152 

Phosphorus 153 

Manganese 153 

Sulphur 153 

Acid  and  Basic  processes  compared 154 

Recent  Advances  in  Open  Hearth  Practice 

Tilting  furnaces 155 

The  Talbot  process 156 

The  Bertrand-Thiel  process 157 

CHAPTER  XVI 
Further  Treatment  of  Iron  and  Steel 

Casting  the  ingots 158 

Stripping  the  ingots 159 

The  soaking  pits 160 

Forging 161 

The  Blooming  or  slabbing  mill 161 

The  three-high  mill 163 

The  continuous  mill 164 

Hammer  forging 164 

Press  forging ^4 

Reheating 165 

Tempering !66 

Development  of  surface  hardness — case  hardening 1 68 

Specifications 168 

CHAPTER  XVII 

Copper,  Ores,  Properties,  Etc. 

Historical 170 


CONTENTS  xi 

Ores 

Native  copper !  70 

Chalcopyrite !  70 

Chalcocite jyo 

Tetrahedrite 171 

Malachite jyr 

Cuprite  and  melaconite 17! 

Properties 

Pure  copper jyj 

Effect  of  impurities ij2 

Chemical  properties 173 

Preliminary  Treatment 

Heap  roasting !74 

Stall  roasting x^tj 

Furnace  roasting 176 

Hand  reverberatory  furnaces 176 

Mechanical  furnaces 1 78 

Shaft  furnaces xgo 

Chemistry  of  roasting 182 

CHAPTER  XVIII 

Copper  Smelting 

Reverberatory  Smelting 

Fusion  for  matte 184 

Fusion  for  blue  or  white  metal 187 

Fusion  for  blister  copper 187 

Chemistry  of  reverberatory  smelting 188 

Blast  Furnace  Smelting 

Forehearths 192 

The  process 192 

Treatment  of  matte  in  Bessemer  converters 193 

The  process 195 

Pyritic  Smelting 

Elimination  of  impurities  during  smelting 197 

Extraction  of  Copper  in  the  Wet  Way 

The  sulphate  process 199 

The  chloride  process 200 

CHAPTER  XIX 

Copper  Refining 

The  Furnace  Process 

Elimination  of  impurities 202 


Xll  CONTENTS 

Electrolytic  Process 

General  principles  of  electrolysis 203 

Refining  plant  and  process 205 

Purification  of  the  electrolyte - 207 

Treatment  of  the  anode  mud 208 

CHAPTER  XX 
Lead,  Ores,  Properties,  Etc. 

History 209 

Ores 

Galena 209 

Cerusite 209 

Pyromorphite 209 

Properties 

Effect  of  impurities 210 

Chemical  properties 211 

Preparation  of  Lead  Ores  for  Smelting 

Roasting 212 

The  process 212 

CHAPTER  XXI 

Lead  Smelting 

Reverberatory  Smelting 

The  process 215 

Hearth  Smelting 
The  process 216 

Blast  Furnace  Smelting 

Chemistry  of  lead  smelting 220 

Lead  fume 222 

CHAPTER  XXII 
Lead  Refining 

Softening 
Desilverizing 

1.  By  the  Pattinson  process 225 

2.  By  the  Parkes  process 227 

Desilverization ...   227 

Distillation 228 

Electrolytic  Refining 
CHAPTER  XXIII 

Zinc 
History 23I 


CONTENTS  Xlll 

Ores 

Sphalerite 231 

Smithsonite 231 

Willemite 231 

Calamine 231 

Franklinite 231 

Properties 

Chemical 232 

Impurities  in  zinc 232 

Preparation  of  Zinc  Ores  for  Smelting 

Mechanical  concentration 233 

Zinc  Smelting 

Manufacture  of  retorts  and  condensers 234 

Form  and  size  of  retorts 235 

Drying  and  annealing  retorts 236 

The  distillation  furnace 236 

The  distillation  process 237 

Refining  Spelter 239 

CHAPTER  XXIV 

Tin  and  Mercury 
Tin 

Cassiterite 240 

Properties " 240 

Smelting 241 

Refining 241 

Uses 242 

Mercury 

Properties 242 

Smelting 243 

Uses 244 

CHAPTER  XXV 
Silver 
Ores 

Native  • 245 

Argentite 245 

Horn  silver 245 

Tetrahedrite 245 

Properties 

Chemical  properties . .  .• 245 


XIV  CONTENTS 

Extraction  of  Silver 

1.  Smelting 246 

2.  Amalgamating 246 

Crushing 247 

Chloridizing  in  the  dry  way '. 247 

Chloridizing  in  the  wet  way 247 

The  patio  process 248 

The  Washoe  process 249 

Barrel  amalgamation 253 

Chemistry  of  Chloridizing  and  amalgamating 254 

3.  Leaching 255 

Ziervogel  process 255 

Augustin  process 255 

Patera  process 255 

Russell  process 256 

Cyanide  process 257 

Silver  Refining 

CHAPTER  XXVI 
Gold 

Ores 258 

Properties 258 

Chemical  properties 259 

Extraction  of  Gold 

1 .  Washing 259 

2.  Smelting 260 

3.  Amalgamating 260 

Hydraulicing    260 

Dredging 261 

Milling 263 

4.  Leaching 264 

Plattner  process 264 

Cyanide  process 264 

Electro-cyanide  processes 268 

Refining  Gold 

By  chlorine 270 

By  sulphuric  acid 270 

By  aqua  regia 270 

By  electrolysis 271 

CHAPTER  XXVII 
Nickel,  Aluminum,  Manganese  and  Rarer  Metals 

Nickel 

Ores 272 


CONTENTS  XV 

Properties 272 

Extraction  of  nickel 273 

Cobalt 275 

Aluminum 

History 275 

Ores 276 

Properties  - 276 

Aluminum  smelting 276 

Manganese 

Ores 278 

Properties 278 

Smelting 278 

Rarer  Metals 

Chromium 279 

Tungsten 279 

Molybdenum * ....   280 

Vanadium 280 

Platinum .   280 

CHAPTER  XXVIII 
Alloys 

Properties 282 

Constitution 283 

Cooling  curves 284 

Conditions  necessary  for  alloying 285 

The  Preparation  of  Alloys  on  the  Industrial  Scale 

Tables  showing  composition 287 

Notes  on  the  Manufacture  of  Alloys 

Alloy  steels 288 

Brass 289 

Other  alloys 289 

Welding 

Electric  welding 290 

Thermit  welding 290 

Plating 

Tin  plating 291 

Zinc  plating 292 

The  dipping  process 293 

The  electrolytic  process    293 

Plating  with  other  metals 294 


ILLUSTRATIONS 

Figure  Page 

1  Pulling  test 3 

2  Riehle  testing  machine opposite  4 

3  Tests  of  fire-clay 13 

4-5  Parr  calorimeter 17-18 

6  Principle  of  Bristol  pyrometer 22 

7  Bristol  indicating  and  recording  unit opposite  22 

8  Charcoal  mound 31 

9-10          Beehive  coke  oven 33~34 

1 1  Otto-Hoffman  coke  oven 36 

12  Diagram  of  coking  process 39 

13  Siemen's  gas  producer 40 

14  Morgan  gas  producer opposite  4 1 

15  Blake  ore  crusher 49 

16  Gates  ore  crusher opposite  50 

17  Stamp  battery opposite  51 

18  Stamp  mill  mortar 52 

19  Chilian  mill opposite  53 

20  Huntington  mill opposite  52 

21  Jig 54 

22  Frue  vanner opposite  55 

23  Principle  of  Wetherill  separator opposite  57 

24  Wetherill  separator opposite  58 

25  Cleveland  kiln 61 

26  Iron  blast  furnace 78 

27  Iron  blast  furnace  plant 86 

28  Bosh  construction 88 

29  Gayley  plate 89 

30  Cooler  and  tuyere 90 

31  Brown  distributor opposite  91 

32  Dust  catcher 92 

33  Hot  blast  stove 94 

34  Blowing  engine opposite  96 

35-36-37     Pyrometer  records 102 

38  Arrangement  for  skimming  iron 106 

39  Pig  bed 107 

40  Showing  manner  of  cooling  in  casting in 

41  Whiting  cupola  and  details 114 

42  Casting  roll  in  chill 117 

43  Showing  effect  of  chill 117 

44  Catalan  forge 122 

45  American  bloomary 123 


ILLUSTRATIONS  XV11 

46  Muffles  for  experimental  furnace 125 

47  Reverberatory  furnace 127 

48  Principle  of  rotary  squeezer 129 

49  Cementation  furnace 132 

50  Bessemer  steel  converter 139 

5 1  Showing  method  of  rotating  converter 140 

52  Steel-pouring  ladle 142 

53-54           Open  hearth  furnace 146 

55  Diagram  of  open  hearth  heat 155 

56  Campbell  furnace 156 

57  Ingot  molds  and  bogie 159 

58  Universal  slabbing  mill opposite  162 

59  Wobbler  and  coupling  box  for  rolls 162 

60  Three-high  mill 163 

6 1  Steam  hammer opposite  164 

62  Hand  reverberatory  furnace    177 

63  Brown  roaster 179 

64-65  Herreshoff  furnace 180-181 

66-67          Copper  matting  furnace 185-186 

68  Round,  copper  blast  furnace 190 

69  Rectangular  copper  blast  furnace opposite  191 

70  Bisbee  converter opposite  193 

7 1  Principle  of  electrolysis 204 

72-73           Arrangement  of  electrodes  in  copper  refinery 206 

74  English,  lead  reverberatory  furnace 215 

75  Lead  blast  furnace 218 

76-77           Parkes  desilverizing  plant 227 

78  Cupellation  furnace 229 

79  Zinc  distillation  furnace 237 

80  Mercury  furnace 244 

81  Amalgamating  pan 251 

82  Silver  concentrating  and  amalgamating  plant. -opposite  254 

83  Gold  dredge 262 

84  Gold  precipitating  boxes    267 

85  Aluminum  reduction  furnace 277 

86  Tin  cooling  curve 285 

87  Tin-copper  alloy  cooling  curve  •  •  •    286 

88  Tinning  pot 292 


THE 


UNIVERSITY 


OF 


CHAPTER  I 


THE  PHYSICAL  PROPERTIES  OF  THE  METALS 

The  value  of  metals  depends  almost  entirely  upon  their  phys- 
ical properties.  Their  great  strength  and  rigidity,  together  with 
their  pleasing  appearance,  have  commended  them  for  economic  and 
ornamental  uses  from  the  earliest  times.  To  the  manufacturers  of 
to-day,  who  supply  the  markets  with  the  useful  metals,  a  knowledge 
of  these  properties,  and  of  the  ways  in  which  they  may  be  devel- 
oped and  improved,  is  indispensable.  Some  of  these  are  well 
known  as  characteristics  of  all  the  common  metals,  while  others 
are  observed  only  when  the  metal  is  subjected  to  peculiar  condi- 
tions. The  subject  is  taken  up  here  in  a  general  way,  and  the 
properties  are  carefully  defined  without  reference  to  any  specific 
metal.  As  the  individual  metals  are  studied,  reference  will  be 
made  to  their  characteristics  and  acquired  properties. 

Fracture. — The  fracture,  or  appearance  of  the  freshly  broken 
surface  of  a  metal  is  to  some  extent  an  index  to  its  other  proper- 
ties. Each  metal  has  its  characteristic  fracture,  and  the  same 
metal  under  varying  conditions  of  purity  and  mechanical  treat- 
ment presents  fractures  differing  accordingly.  In  some  instances 
the  quality  of  a  metal  may  be  inferred,  and  an  approximate  esti- 
mate made  of  the  amount  of  impurities  it  contains,  by  simply  ex- 
amining its  fracture. 

When  metals  cool  from  a  state  of  fusion,  like  most  other  solidi- 
fying substances,  they  tend  to  form  crystals.  But  the  conditions 
attending  the  cooling  of  metals  do  not,  as  a  rule,  permit  of  any 
high  degree  of  crystallization.  As  seen  by  the  naked  eye,  the 
structure  appears  granular  in  most  instances,  but  upon  polishing 
and  carefully  etching  a  surface,  the  crystalline  structure  may  be 
seen  with  the  aid  of  a  microscope.  The  structure  of  metals,  as 
shown  by  their  fracture,  is  affected  by  any  impurities  present,  by 
heat  treatment  and  by  such  mechanical  treatment  as  hammering 
or  rolling. 


2  METALLURGY 

Tenacity. — By  tenacity  is  meant  the  property  of  resisting  a  ten- 
sile or  stretching  force.  The  extent  to  which  a  metal  will  resist 
being  pulled  apart  is  termed  its  tensile  strength.  The  tenacity  of 
metals  varies  with  the  composition,  temperature  and  treatment,  it 
being  improved  in  most  metals  by  the  addition  of  certain  other 
elements  in  the  proper  proportions. 

Most  of  the  metal  that  comes  on  the  market  is  bought  under 
certain  specifications  relative  to  its  physical  properties.  These 
properties  are  largely  interpreted  from  chemical  analysis,  but  in 
many  instances  mechanical  testing  is  required.  By  this  means 
the  effort  is  made  to  expose  a  piece  of  the  metal,  representing  the 
whole,  to  strains  similar  to  those  encountered  in  actual  service, 
the  force  applied  being  measured,  and  its  effect  upon  the  test- 
piece  noted.  The  test-piece  is  broken  if  it  is  desirable  to  know 
the  ultimate  strength.  The  tenacity  is  of  greatest  importance 
in  many  instances,  and  it  is  determined  directly  by  breaking  a  bar 
of  the  metal  in  a  machine  which  indicates  the  force  used. 

Elasticity. — Any  substance  which  is  capable  of  returning  to  its 
original  form  and  size  after  being  distorted  is  said  to  be  elastic. 
A  substance  that  is  perfectly  elastic  will  retain  this  property  after 
being  distorted  an  infinite  number  of  times.  Liquids  and  gases 
are  perfectly  elastic,  but  solids  are  only  approximately  so.  It  is 
a  well  known  fact  that  metal  springs,  after  long  usage  become 
"set,"  their  original  shape  being  permanently  altered.  Glass  is 
shown  to  be  elastic  by  bending  a  straight  rod,  which  will  remain 
straight  afterward.  If,  however,  the  rod  is  supported  at  the 
ends  in  a  horizontal  position,  with  a  weight  attached  at  the  middle, 
and  allowed  to  remain  for  a  few  weeks,  it  will  be  permanently  bent. 

When  the  elasticity  of  a  metal  has  been  destroyed  to  such  an 
extent  that  it  shows  little  or  no  tendency  to  return  to  its  original 
form  it  is  said  to  be  plastic.  Some  metals,  such  as  lead  and 
gold,  are  naturally  plastic.  These  are  less  of  the  nature  of  true 
solids. 

The  extent  to  which  a  metal  can  be  stretched  or  compressed 
without  rupture  is  termed  its  elastic  limit.  This  value  may  be 
measured  and  expressed  numerically  as  the  units  of  force  neces- 
sary to  rupture  a  bar,  the  area  of  whose  cross-section  is  given.  If 


PHYSICAL    PROPERTIES    OF    METALS  3 

the  composition  of  the  bar  is  homogeneous,  and  it  is  of  uniform 
thickness  between  the  points  at  which  the  force  is  applied,  equal 
additions  of  force  will  produce  equal  elongations  or  depressions,, 
until  the  elastic  limit  is  reached. 

The  spring  balance  serves  to  illustrate  the  above  statement. 
The  pointer,  moving  over  a  scale  or  dial  is  attached  to,  or  operated 
by  the  loose  end  of  a  spring.  The  other  end  of  the  spring  being" 
fastened,  it  is  compressed  or  stretched  when  weights  are  placed  on 
the  pan.  The  pointer  is  seen  to  move  equal  distances  for  equal  ad- 
ditional weights. 

From  what  has  been  said  it  is  clear  that  the  amount  of  force 
required  to  produce  any  elongation,  within  the  elastic  limit,  can 
be  estimated,  provided  it  is  known  how  much  is  required  to 
produce  a  given  elongation.  If  the  elasticity  remained  perfect, 


Fig.  i. 

the  force  necessary  to  double  the  length  of  a  bar  is  termed  its 
modulus  of  elasticity.  Suppose,  for  example,  that  a  bar  of  steel 
is  stretched  from  eight  inches  to  8.03  inches  by  a  force  of  126,000 
pounds.  The  modulus  of  elasticity  would  be — 

0.03  :8  ::  126,000  :x,  or  33,600,000  pounds. 
This  value  is,  of  course,  purely  theoretical,  as  no  metal  has  so  high 
a  limit  of  elasticity. 

Testing  Machines. — Machines  are  now  regularly  used  for  break- 
ing bars  by  direct  pull,  the  stress  used  being  measured  and  re- 
corded. Fig.  i  represents  a  "pulling  test"  before  and  after  it 
is  broken.  The  size  and  shape  of  these  test-bars  is  not  fixed, 
but  the  one  described  is  the  best  form  for  general  purposes.  It 
is  turned  down  on  a  lathe  to  a  uniform  diameter,  which  is  ac- 
curately measured  with  a  micrometer.  Punch  marks  are  made 


4  METALLURGY 

at  the  points  A  A,  which  are  usually  eight  inches  apart.  The  bar 
is  grasped  by  the  machine  at  the  points  B  B.  After  the  bar  has 
been  broken,  measurements  are  again  taken  of  the  length  and 
the  diameter  at  the  point  of  fracture,  to  ascertain  the  elongation 
and  contraction. 

The  primary  object  in  making  the  pulling  test  is  to  determine 
elasticity  and  tensile  strength,  but  other  valuable  information  is 
gained,  as  shown  below. 

The  construction  of  a  testing  machine  is  shown  in  Fig.  2.  The 
base  of  the  machine  consists  of  a  substantial,  cast  iron  box,  M, 
enclosing  the  driving  mechanism.  The  power  is  transmitted  by 
gearing  to  the  two  large  screws,  one  of  which  is  visible,  R.  By 
turning  these  screws  the  pulling  head  is  moved.  The  top  and  pull- 
ing heads,  I  I,  are  fitted  with  hardened  steel  wedges  for  gripping 
the  specimens.  The  top  head  is  supported  on  two  cast  iron 
columns  which  are  bolted  to  the  weighing  table,  T.  The  table 
rests  upon  the  two  main  levers  of  the  weighing  mechanism.  One 
of  the  levers  is  enclosed  within  the  other,  A,  and  each  lever 
branches  into  a  Y  to  give  a  broad  support  for  the  table.  The 
friction  at  the  points  of  support  is  minimized  throughout  the 
weighing  apparatus  by  the  use  of  steel  knife  edges  resting  on 
steel  plates.  The  intermediate  lever,  B,  and  its  connection  with 
the  main  lever  and  the  beam,  C,  are  clearly  shown  in  the  cut. 
With  this  system  of  levers  the  strain  exerted  upon  the  specimen 
may  be  counterbalanced  by  moving  the  weight,  W,  along  the 
beam.  The  stress  is  measured  in  pounds  or  kilograms  which  are 
marked  on  the  beam. 

Transverse  tests  may  be  made  by  aid  of  the  V-shaped  tools,  one 
of  which  is  shown  attached  to  the  under  side  of  the  pulling  head 
and  the  other  two  set  up  on  the  weighing  table.  The  tools  upon 
the  table  are  set  at  equal  distances  from  the  middle,  and  the 
specimen  is  supported  on  these  in  the  horizontal  position.  The 
pulling  head  is  lowered  upon  the  specimen  until  it  is  sufficiently 
bent  or  broken. 

Crushing  tests  are  made  by  placing  the  specimen  between  two 
dies,  one  of  which  rests  upon  the  center  of  the  table  and  the  other 
is  attached  to  the  pulling  head. 


Fig.  2— Riehle,  Standard  Testing  Machine. 


PHYSICAL    PROPERTIES    OF    METALS  5 

Toughness. — The  resistance  which  a  metal  offers  to  being  pulled 
apart  after  its  elastic  limit  has  been  reached  is  due  to  tough- 
ness. The  tough  metals  are  scarcely  elastic — if  either  one  of  these 
properties  is  developed  in  a  metal,  it  is  usually  done  at  the  ex- 
pense of  the  other.  As  a  rule,  metals  are  toughest  when  in  the 
pure  state. 

An  expression  for  toughness  in  a  metal  is  gained  from  the 
mechanical  test  described  above.  It  is  observed  that  the  toughest 
bars  give  the  greatest  percentage  of  elongation  and  contraction. 
The  figures  for  these  values  are  an  expression  for  the  toughness 
of  the  metal  tested.  Toughness  is  further  tested  by  what  is  known 
as  the  "cold  bending  test."  The  test-bar  is  bent,  without  heating, 
at  a  sharp  angle  until  the  ends  meet,  or  overlap.  If  there  is  not 
considerable  toughness  the  bar  will  either  break  or  rupture  on  the 
outer  surface  where  the  greatest  strain  is  imposed.  Although 
no  numerical  expression  is  obtained,  this  test  is  invaluable  to  metal 
workers  and  engineers  as  a  guide  to  the  purity  and  quality  of  some 
grades  of  iron.  Toughness  is  greatly  influenced  by  heat. 

Malleability. — Metals  which  can  be  permanently  extended  with- 
out fracture  are  termed  malleable.  Degree  of  malleability  is 
shown  by  the  thinness  of  the  rheet  into  which  the  metal  can  be 
hammered.  As  a  rule,  this  property  is  most  perfect  in  a  metal 
when  it  is  pure,  and  it  is  generally  increased  with  temperature. 
If  hardness  or  elasticity  is  developed  in  a  metal,  its  malleability 
is  diminished.  It  is  chiefly  upon  this  property  that  the  processes 
of  rolling  and  hammering  depend. 

Ductility. — The  ductile  metals  are  those  which  are  capable  of 
being  drawn  into  wire.  The  property  of  ductility  depends  mostly 
upon  tenacity,  malleability  and  toughness.  It  will  be  seen  by 
referring  to  the  table  (p.  8)  that  the  malleable  metals  are  the  most 
ductile.  Most  metals  show  great  changes  in  their  ductility  with 
changes  in  temperature.  The  property  is  improved  by  annealing. 

Wire  Drazi'ing. — Wire  is  made  by  drawing  a  bar  of  metal,  some- 
what larger  in  diameter  than  the  resulting  wire,  through  funnel- 
shaped  holes  in  dies  of  hard  steel.  A  number  of  dies  may  be 
employed,  depending  upon  the  size  to  which  the  wire  must  be  re- 


6  METALLURGY 

duced.  The  end  of  the  bar  is  first  sharpened  until  it  will  pass 
through  the  openings,  and  is  gripped  by  the  forceps  of  the 
machine.  The  pressure  that  is  brought  to  bear  by  the  funnel- 
shaped  holes  is  about  the  same  in  effect  as  that  of  rolling,  while 
the  stretching  force  compels  extension  in  the  one  direction.  The 
tenacity  of  the  finished  wire  is  tried,  since  it  sustains  the  entire 
drawing  force. 

Flow. — The  term  flow  relates  to  the  molecular  movements  of 
metals  in  the  solid  state.  With  the  exception  of  mercury,  none 
of  the  metals  flow  in  the  usual  sense  of  the  term,  but  all  of  them 
become  mobile  under  sufficient  pressure,  i.  e.,  they  flow  as  viscid 
liquids  do.  This  property  is  associated  with  that  of  malleability. 
It  is  made  use  of  in  various  manufactures,  examples  of  which  are 
the  manufacture  of  lead  pipe  and  coin  striking. 

Brittleness. — The  brittle  metals  are  those  which,  relatively 
speaking,  are  neither  malleable  nor  ductile.  Such  metals  are 
usually  hard,  but  can  be  easily  broken,  and  in  some  cases 
powdered  under  a  hammer.  Brittleness  is  opposed  to  toughness, 
and  is  rarely  desired  in  any  metal.  It  is  influenced  chiefly  by 
foreign  elements,  but  it  frequently  develops  where  strains  are 
applied  in  different  directions,  or  in  metal  that  is  subjected  to 
violent  shocks.1  Changes  in  temperature  have  a  marked  effect 
upon  the  brittleness  of  metals.  The  best  way  to  remove  brittle- 
ness  is  by  annealing. 

Drop  Testing. — Metals  are  examined  for  brittleness  by  means 
of  the  "drop  test."  The  test-piece  is  subjected  to  blows  from  a 
hammer  of  a  certain  weight  dropped  from  a  stated  height. 

Hardness. — In  determining  the  hardness  of  metals  the  dia- 
mond is  taken  as  10,  the  other  substances  being  referred  to  that. 
Hardness  is  opposed  to  flow,  and  is  especially  required  in  tools 
and  the  wearing  parts  of  machinery.  It  is  not  a  common  prop- 
erty of  pure  metals,  but  in  most  instances  requires  to  be  developed. 

Fusibility  and  Volatility. — All  the  metals  are  fusible  and  all 
1  Car  axles  may  break  after  long  service,  the  fracture  showing  a  crys- 
talline structure  which  the  metal  did  not  have  when  the  axle  was  made. 
The  pistons  of  large  steam  hammers  sometimes  break  after  being  used  but  a 
short  time. 


PHYSICAL    PROPERTIES    OF    METALS  7 

are  volatile.  Some  are  infusible,  and  but  few  are  volatile  at 
ordinary  furnace  temperatures.  The  metals  of  commerce  may 
have  much  lower  melting  points,  as  a  result  of  impurities.  In 
all  processes  for  extracting  metals  by  smelting,  advantage  is 
taken  of  their  fusibility.  It  is  of  importance  to  know  the  melt- 
ing points  of  metals,  and  as  well  their  behavior  in  the  liquid 
state,  in  connection  with  the  foundry  industries. 

Diffusion. — Most  metals  have  the  property  of  forming  homo- 
geneous mixtures  with  other  metals.  This  is  known  as  the  alloy- 
ing property  or  the  property  of  diffusion,  and  the  mixtures  are 
called  alloys.  Some  metals  alloy  with  great  readiness  and  in 
all  proportions,  while  with  others  it  is  very  difficult  to  bring 
about  any  union  at  all.  It  has  been  found  possible  to  develop 
properties  in  alloys  to  a  degree  which  has  never  been  attained 
with  any  single  metal.  As  might  be  supposed,  some  of  the  prop- 
erties of  alloys  are  intermediate  between  those  of  the  constituent 
metals,  but  this  is  not  true  of  all. 

It  is  generally  understood  that  metals  diffuse  only  when  one 
or  both  are  in  the  liquid  state,  but  it  is  possible  with  moderate 
pressure  to  make  plastic  metals  diffuse  slightly,  and  under  enor- 
mous pressure  the  more  brittle  metals  may  unite.  This  obviously 
makes  use  of  the  flowing  property.  The  subject  of  alloys  is 
more  fully  discussed  in  Chapter  XXVIII. 

Welding. — This  is  the  property  of  uniting  without  fusion.  The 
requirements  for  welding  are  that  the  pieces  to  be  united  shall 
be  in  a  plastic  condition,  fairly  pure,  and  the  faces  to  come  in 
contact  clean.  Enough  pressure  must  be  applied  to  bring  the 
molecules  into  intimate  contact.  A  hard  metal  may  be  welded 
by  heating  it  until  it  becomes  plastic.  If  a  coating  of  oxide 
forms,  it  must  be  removed.  As  a  rule,  the  pieces  to  be  welded 
must  be  of  the  same  kind  of  metal.  Exceptions  are  found  with 
iron  and  platinum,  lead  and  tin  and  some  others, 

Occlusion. — By  this  term  is  meant  the  absorption  and  retention 
of  gas.  The  property  varies  greatly  with  the  metals,  and  the 
same  metal  absorbs  different  quantities  of  the  different  gases. 
As  a  rule,  gases  are  dissolved  most  freely  when  the  metal  is  pure 
and  in  the  molten  state.  On  cooling  most  of  the  gas  is  dis- 


8  METALLURGY 

charged,  often  producing  the  effect  of  boiling,  while  some  is  re- 
tained as  accumulated  bubbles  ("blow-holes")  under  the  harden- 
ing surface,  or  held  by  the  metal  in  "solid  solution."  The  phys- 
ical properties  in  general  are  known  to  be  effected  in  metals  by 
occlusion. 

Conductivity.  —  The  metals  are  the  best  conductors  of  heat  and 
electricity.  The  extended  use  of  the  electric  current  has  led  to 
the  improvement  of  the  conductivity  of  the  metals  used  in  the 
transfer  of  power.  The  property  is  much  altered  by  the  pres- 
ence of  impurities,  only  a  trace  in  some  instances  affecting  it. 
Conductivity  varies  inversely  with  the  temperature  of  the  metal. 

Magnetism.  —  The  magnetic  property  of  iron  has  long  been 
known  and  studied.  It  has  been  discovered  in  some  other  metals 
and  alloys,  but  it  is  much  weaker  in  these  and  is  not  of  practical 
value.  It  is  affected  by  impurities  and  temperature.  Magnetism 
in  iron  will  be  dealt  with  under  the  study  of  that  metal. 

Density.  —  One  of  the  distinguishing  features  of  metallic  sub- 
stances is  their  superior  density,  or  specific  gravity.  While  it  is 
true  that  metals,  taken  as  a  class,  are  heavier  than  othen  sub- 
stances, there  are  exceptions,  and  there  is  no  relationship  between 
the  density  and  the  other  properties  of  metals.  This  property  is 
made  use  of  in  practically  all  processes  of  metal  extraction. 

The  following  groups  show  the  orders  of  tenacity,  malleability 
and  ductility  : 

TENACITY. 

1  Steel  4    Copper  7    Zinc 

2  Nickel  5     Aluminum  8    Tin 

3  Iron  6    Gold  9    Lead 


1  Gold  5  Tin  8  Zinc 

2  Silver  6  Platinum  9  Iron 

3  Copper  7  Lead  10  Nickel 

4  Aluminum 

DUCTILITY. 

1  Gold  5  Iron  8  Zinc 

2  Silver  6  Nickel  9  Tin 

3  Platinum  7  Copper  10  Lead 

4  Aluminum 


PHYSICAL   PROPERTIES   OF    METALS 


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CHAPTER  II 


THE  REFRACTORY   MATERIALS  AND  FLUXES 

The  refractory  materials  comprise  all  substances,  natural  or 
prepared,  that  are  practically  infusible.  These  are  indispensable 
to  the  metallurgical  industries.  The  parts  of  furnaces  and  re- 
taining vessels  that  are  exposed  to  high  temperatures  must  be 
constructed  of  such  material  as  will  not  soften  or  be  acted  on 
chemically  by  the  substances  that  come  in  contact  with  them, 
and  the  material  should  not  crack  or  alter  much  in  volume  dur- 
ing heating  and  cooling. 

Classification. — There  are  a  number  of  substances  which  with- 
stand the  action  of  heat  alone  to  a  high  degree,  but  react  chem- 
ically if  certain  other  substances  come  in  contact  with  them.  It 
is  necessary,  therefore,  in  lining  a  furnace  for  any  specific  opera- 
tion to  select  that  material  which  is  least  affected  by  the  slags  or 
mixtures  peculiar  to  that  operation.  The  refractories  are  classi- 
fied, according  to  their  chemical  properties,  as  acid,  basic  and 
neutral  materials.  It  is  a  well  known  fact  that  acids  and  bases 
neutralize  each  other  mutually  with  the  formation  of  new  com- 
pounds. An  acid  lining  would  be  corroded  and  melted  out  if 
the  mixtures  of  the  furnace  were  basic  in  character,  and  vice 
versa.  The  neutral  refractories  have  practically  no  reaction  with 
either  acid  or  basic  substances. 

ACID  MATERIALS 

Silica. — This  is,  strictly  speaking,  the  only  acid  refractory  sub- 
stance used.  The  others  owe  their  acid  character  to  the  presence 
of  silica.  It  occurs  nearly  pure  as  quartz  and  in  combination  with 
metallic  oxides.  The  fusion  point  of  silica  is  very  high,  though 
it  is  entirely  melted  in  the  electric  furnace.  It  expands  slightly 
when  heated,  but  is  otherwise  practically  unaltered  at  ordinary 
furnace  temperatures.  Heated  in  contact  with  metallic  oxides 
(basic  substances),  it  forms  silicates,  many  of  which  are  readily 
fused.  Silica,  as  a  refractory  material,  is  used  chiefly  in  the 
form  of  loose  sand  or  compressed  bricks. 


REFRACTORY    MATERIALS    AND    FLUXES  II 

Sand  is  essentially  pure  silica,  arising  from  the  decomposition 
of  rocks,  but  it  may  contain  a  quantity  of  clay  and  other  foreign 
matter.  It  is  chiefly  used  in  the  bottoms  of  furnaces  and  for  beds 
or  molds  into  which  metal  is  cast. 

Silica  Brick  are  prepared  either  from  crushed  siliceous  rock  or 
from  sand.  The  fine  material  is  mixed  with  a  small  amount  of 
alumina  or  lime,  pressed  into  shape,  carefully-  dried  and  then 
ignited  at  a  high  temperature.  The  amount  of  lime  or  alumina 
added  is  very  small  and  is  not  sufficient  to  react  with  the  over- 
whelming mass  of  silica,  only  the  surface  of  the  grains  being 
affected.  These  having  been  brought  into  close  contact  by  the 
powerful  pressure  previously  applied,  are  now  cemented  together 
by  the  silicate  formed.  Silica  brick  are  hard  and  durable,  though 
lacking  in  toughness.  They  stand  furnace  temperatures  well, 
expanding  slightly  when  heated. 

Clay. — This  important  substance  is  essentially  a  hydrated  sil- 
icate of  alumina.  It  is  extremely  variable  in  composition,  some- 
times containing  an  excess  of  free  silica  and  sometimes  an  excess 
of  alumina.  The  impurities  often  found  in  clay  are  the  oxides 
of  iron,  calcium,  magnesium,  titanium  and  the  alkalies.  In  the 
purer  clays  these  minor  ingredients  have  been  dissolved  and 
leached  out  by  natural  processes.  Free  silica  is  usually  in  the 
excess,  some  specimens  carrying  so  much  silica  as  not  to  be  dis- 
tinguished by  casual  inspection  from  sand.  The  compositions  of 
clays  from  some  important  deposits  in  the  United  States  are 
given  in  Chapter  XXIII. 

Clay  is  formed  by  the  natural  decomposition  of  feldspar.  Some 
clays  appear  to  lie  in  the  position  occupied  by  the  original  rock, 
but  the  most  important  deposits  are  alluvial. 

The  pure  or  refractory  clays  are  commonly  called  fire-clays. 
The  wide  use  of  clay  is  largely  due  to  its  becoming  plastic  and 
cohesive  when  wet.  For  this  reason  bricks  and  crucibles  may  be 
manufactured  from  it  without  the  use  of  a  binding  material. 
When  ignited .  sufficiently  to  drive  off  the  combined  water,  clay 
loses  its  plasticity,  but  if  pressed  before  ignition  it  cements  itself 
into  a  hard  mass.  Clay  shrinks  during  ignition  on  account  of 


12 


METALLURGY 


the  loss  of  water.  This  combined  water  can  not  be  restored  after 
ignition.  For  this  reason  burnt  and  raw  clay  are  often  mixed  by 
manufacturers  to  lessen  shrinkage.  Clay  is  the  furnace  builder's 
mortar.  In  building  substantial  furnace  walls  the  bricks  are  set 
in  fire-clay,  and  sometimes  it  is  plastered  over  the  walls  to  form 
a  seamless  lining. 

The  most  refractory  clays  are  those  containing  an  excess  of 
alumina.  The  impurities  (basic  oxides),  though  they  might  be 
highly  refractory  when  isolated,  have  a  softening  effect  on  the 
clay  on  account  of  their  chemical  action.  Alumina,  being  a 
weak  base,  does  not  form  an  easily  fusible  compound  with  silica, 
but  with  another  base,  such  as  lime,  an  easily  fusible,  compound 
silicate  may  be  formed.  Sulphide  of  iron  is  sometimes  met  with 


Fig.  3— Showing  Relative  Fusibility  of  Different  Clays. 

in  clay,  -  existing  as  small  grains  or  crystals.  This  is  highly  ob- 
jectionable, since  on  being  heated  strongly  the  sulphide  is  con- 
verted into  ferrous  oxide,  which  in  turn  combines  with  silica. 
The  ferrous  silicate  formed  is  then  fused  out,  leaving  a  cavity. 
The  amount  of  ferric  oxide  that  is  allowable  in  a  good  fire-clay  is 
a  disputed  point.  As  much  as  2  per  cent,  is  not  unusual  and 
does  not  seem  to  be  detrimental.  The  lime,  magnesia  and  alka- 
lies together  should  not  amount  to  more  than  2  per  cent. 

Testing  Fire-Clay. — A  practical  test  of  the  refractoriness  of 
clays  may  be  made  as  follows:  Each  sample  to  be  examined  is 
ground  fine,  well  mixed  and  made  into  a  stiff  dough.  From  each 
is  then  made  a  small  pyramid,  the  sides  measuring  *4"  at  tne  base,, 
the  height  being  3".  After  carefully  drying,  the  pyramids  are 
placed  in  a  muffle  furnace,  the  temperature  of  which  can  be 


REFRACTORY    MATERIALS    AND    FLUXES  13 

raised  as  desired,  and  recorded  by  means  of  a  pyrometer.  As 
the  temperature  is  raised  the  tendency  toward  fusion  is  marked 
by  the  appearance  of  the  pyramids.  The  ones  containing  the 
purest,  or  most  refractory  clay,  remain  straight,  while  those 
containing  fusible  matter  show  a  tendency  to  curl,  as  shown  in 
the  figure.  This  is  due  to  partial  fusion.  This  method  of  testing 
the  refractory  power  of  a  clay  is  preferred  to  the  calculated  value, 
based  on  analysis.  To  ascertain  directly  how  much  fluxing  matter 
can  be  allowed  in  clay  for  any  particular  purpose,  a  pure  clay  may 
be  mixed  with  increasing  percentages  of  the  flux  and  tested  as 
above.1 

Granister. — This  is  a  natural  sandstone,  containing  from  85  to 
95  per  cent,  of  silica,  the  rest  being  mainly  alumina.  It  is  either 
cut  and  used  in  the  form  of  blocks  or  ground  and  rammed  in 
place  as  mortar.  The  principal  application  of  ganister  is  in  lining 
Bessemer  converters  for  the  acid  process.  Mica  schist  and  other 
stones  containing  a  large  excess  of  silica  are  much  used  in  this 
country. 

BASIC  MATERIALS 

Magnesia. — The  mineral  magnesite,  or  carbonate  of  magnesia, 
is  frequently  met  with,  associated  with  serpentine  and  other  sili- 
ceous rocks.  Large  known  deposits  are  rare,  though  some  im- 
portant recent  discoveries  have  been  made.  The  main  source  of 
magnesite  in  this  country  is  California,  where  some  of  great  purity 
is  found.  More  is  imported  from  Greece  and  Styria. 

When  magnesite  is  ignited  at  high  temperature  it  gives  off  car- 
bon dioxide,  and  the  residue  is  magnesium  oxide  or  magnesia. 
This  substance  is  highly  refractory,  and  it  is  the  most  satisfac- 
tory material  known  for  some  purposes.  It  is  crushed  and  used 
on  the  hearths  of  basic  furnaces  or  manufactured  into  bricks  for 
constructing  the  walls.  Magnesia  has  no  binding  property  of  its 
own,  but  strong  bricks  are  made  by  mixing  with  it  a  small  quan- 
tity of  siliceous  material  and  compressing.  The  price  of  mag- 
nesia precludes  its  more  general  adoption. 

Lime  is  made  from  calcite  or  limestone,  just  as  magnesia  is 
prepared  from  magnesite.     It  is  even  more  infusible  than  mag- 
1  For  a  full  discussion  of  this  subject  see   "The  Collected  Writings   o 
Hermann  A.  Seger,"  I,  p.  224. 


14  METALLURGY 

nesia,  but  its  use  as  a  refractory  is  hardly  important  enough  to 
mention.  Its  strong  affinity  for  water  causes  it  to  attract  moisture 
from  the  atmosphere,  and  as  a  result  it  crumbles.  If,  however, 
lime  be  mixed  with  sufficient  magnesia  a  very  satisfactory  mate- 
rial is  obtained.  Fortunately,  there  is  a  natural  mixture  of  this 
kind,  known  as  dolomite. 

Dolomite. — Like  magnesite  and  limestone,  dolomite  requires 
to  be  strongly  ignited  before  use.  On  account  of  its  abundance, 
dolomite  is  the  most  important  of  the  basic  lining  materials.  It 
is  used  exclusively  in  basic  Bessemer  converters. 

Bauxite. — This  is  the  sesquioxide  of  aluminum  with  varying 
amounts  of  the  corresponding  oxide  of  iron.  The  chief  sources 
in  the  United  States  are  Georgia,  Alabama  and  Arkansas.  Bauxite 
is  highly  refractory  when  free  from  silica,  and  it  is  but  feebly 
"basic.  It  has  proved  itself  an  excellent  lining  material,  and  its 
more  general  adoption  is  expected  if  it  becomes  more  abundant. 

NEUTRAL  MATERIALS 

Graphite. — This  substance,  otherwise  known  as  plumbago  or 
black  lead,  is  an  allotropic  form  of  carbon.  It  is  mined  chiefly  in 
Ceylon,  Siberia  and  Austria.  The  only  mines  in  this  country  of 
any  importance  are  in  New  York.  The  origin  of  graphite  is  not 
known,  though  it  is  supposed  to  be  vegetable.  It  occurs  with 
both  calcareous  and  siliceous  rocks  in  veins  or  lumps,  or  in  the 
form  of  scales  disseminated  through  the  rock.  Graphite  has 
not  been  fused  in  the  isolated  form,  and  only  slight  oxidation 
occurs  at  furnace  temperatures.  In  the  electric  arc  it  burns  freely, 
but  does  not  fuse.  Graphite  would  have  a  very  wide  application 
as  a  refractory  material  if  it  were  not  for  its  high  cost.  Its 
principal  uses  are  in  the  manufacture  of  crucibles  and  bricks  for 
special  purposes,  and  in  foundries.  It  is  used  alone  or  mixed  with 
clay. 

Chromite. — The  use  of  chrome  ore,  or  chrome-iron  ore,  has  been 
restricted  to  a  few  operations  on  account  of  its  scarcity.  It  has 
been  found  most  satisfactory  under  the  severe  test  of  high  tem- 
perature and  in  contact  with  both  acid  and  basic  materials.  Chrome 
ore  is  manufactured  into  brick,  lime  being  used  as  a  binding 
material.  The  analysis  of  one  of  these  bricks,  furnished  by  the 


REFRACTORY    MATERIALS    AND    FLUXES  15 

Harbison- Walker  Refractories  Co.,  of  Pittsburg,  is  here  given: 

SiO2  FeO  A12O3  CaO  MgO  Cr2O3         I<oss  by  Ignition 

5.60          12.92  20.47          3.25  13.52  43.98  0.14 

THE  FLUXES 

In  the  extraction  of  metals  from  their  ores,  and  in  their  sub- 
sequent purification,  the  refuse  matter  of  the  ore  (the  gangue) 
and  the  accumulated  impurities  have  to  be  dealt  with.  These 
substances  are  often  of  a  refractory  nature,  and  remaining  un- 
fused  would  retard  the  process  and  prevent  complete  separation 
of  the  metal.  Advantage  is  here  taken  of  the  behavior  of  acid 
and  basic  substances  toward  each  other.  Some  substance  of  the 
opposite  chemical  character  to  the  gangue  is  added,  and  combina- 
tion ensues  with  the  formation  of  an  easily  fusible  compound. 
The  substance  added  is  called  a  flux  and  the  resulting  compound 
is  slag.  Any  operation  in  which  the  metal  is  withdrawn  in  the 
state  of  fusion  is  termed  smelting.  The  word  cinder  is  used  in- 
terchangeably with  the  word  slag,  but  it  has  a  wider  meaning. 
Cinder,  as  used  in  this  text,  means  refuse  matter  that  is  not  fused. 

Like  the  refractories,  the  fluxes  are  divided  into  the  three 
classes — acid,  basic  and  neutral.  Slags  may  be  made  either  acid 
or  basic  by  adding  to  them  an  excess  of  the  proper  flux.  They 
may  be  made  more  fusible,  without  altering  their  acid  or  basic 
properties  by  adding  a  neutral  substance  having  a  low  melting 
point.  The  common  fluxes  are:  Acid,  silica;  Basic,  lime,  mag- 
nesia, ferrous  oxide,  manganous  oxide  and  alumina  (very  feebly 
basic)  ;  Neutral,  fluorspar. 


CHAPTER  III 


THEORY  OF  COMBUSTION  AND  THERMAL  MEASUREMENTS 

The  term  combustion,  as  used  in  this  treatise,  means  the  rapid 
combination  of  any  substance  with  oxygen.  Any  substance  em- 
ployed for  producing  heat  by  virtue  of  its  combustion  is  a  fuel. 
The  heat  of  combustion  is,  therefore,  due  to  the  union  of  the 
elements  composing  fuels  with  the  element  oxygen. 

The  offices  of  fuels  are  twofold.  In  addition  to  their  being  the 
usual  means  of  obtaining  high  temperatures,  they  often  play  the 
important  part  of  decomposing  the  ores  by  chemical  action  with 
them,  and  liberating  the  metals.  In  this  capacity  they  are  termed 
reducing  agents.  The  term  reduction  generally  means  taking 
oxygen  from  a  compound,  or  the  opposite  of  oxidation.  The 
heat  derived  from  the  combustion  of  fuel  is  not  necessarily  con- 
fined to  the  reactions  with  atmospheric  oxygen,  but  it  may  be 
•due  in  part  to  that  oxidation  which  is  coincident  with  the  reduc- 
tion of  metallic  oxides,  thus: 

(1)  C+02=C02 

(2)  ZnO+'C+O=Zn+COa. 

In  reaction  (i)  the  oxygen  is  entirely  from  the  air,  while  in  re- 
action (2)  half  of  the  oxygen  is  taken  from  the  oxide  of  zinc. 
The  heat  of  oxidation  is  the  same  in  both  cases,  but  in  (2)  heat 
is  absorbed  by  the  reduction  of  zinc  oxide.  A  reaction  in  which 
heat  is  evolved  is  called  exothermic,  and  one  in  which  heat  is 
absorbed  is  called  endo thermic.  It  may  be  said,  in  general,  that 
oxidation  is  exothermic  and  reduction  is  endothermic.  The 
amount  of  heat  derived  from  the  burning  of  fuel  depends  upon 
the  energy  with  which  the  fuel  combines  with  oxygen  and  the 
temperature  produced  depends  upon  the  energy,  rate  of  combus- 
tion and  the  nature  of  the  products  of  combustion. 

The  heating  value  of  a  fuel  is  expressed  as  the  number  of  unit 
weights  of  water  that  one  unit  weight  of  the  fuel  will  raise 
through  one  degree  of  temperature  by  its  combustion.  The  unit 
of  weight  chosen  is  the  kilogram,  and  the  amount  of  heat  neces- 


COMBUSTION  AND  THERMAL  MEASUREMENTS  I? 

•sary  to  increase  the  temperature  of  I  kilogram  of  water  by  I 
degree,  Centigrade,  is  called  one  heat  unit,  or  one  calorie.  The 
heating  value  of  a  fuel  is,  therefore,  called  its  calorific  power. 
This  value  is  determined  directly  by  means  of  the  calorimeter,  or 
by  calculation  from  the  analysis. 

Calorific  Power  by  Experiment. — The  Parr  calorimeter  (Fig. 
.4)  consists  of  two  outer,  insulating  vessels,  B  and  C;  a  two-liter 
can,  A,  for  holding  the  water;  a  rack,  E,  with  a  pivot,  F,  on 


Fig.  4— Parr  Calorimeter.    (Standard  Calorimeter  Co.) 

which  the  cartridge  or  bomb,  D,  is  supported  and  revolved,  and 
a  delicate  thermometer,  T,  for  indicating  the  temperature  of  the 
water.  The  can  is  filled  with  water  and  the  cartridge,  contain- 
ing a  weighed  amount  of  the  fuel  mixed  with  sodium  peroxide 
or  other  oxygenous  chemical,  is  placed  in  position  and  kept  re- 


18 


METALLURGY 


volving  by  aid  of  a  small  motor.  The  mixture  is  ignited  elec- 
trically or  by  dropping  in  a  hot  wire.  Detachable  stirrers  are 
provided  with  the  cartridge  to  keep  the  water  uniformly  mixed. 
The  heat  is  absorbed  by  the  water,  and  from  the  rise  in  tempera- 
ture the  amount  of  heat  evolved  is  calculated. 


-A 


-  5  gives  an  enlarged  view  of  the  cartridge,  which  is  ar- 
ranged for  electric  ignition.  The  ends  of  the  shell,  A,  are  closed 
by  stoppers,  held  in  place  by  means  of  the  screw  caps,  E  and  F. 
The  joints  are  made  tight  by  means  of  rubber  gaskets.  The 
upper  stopper  carries  the  stem,  B,  through  which  a  rod,  J,  in- 


COMBUSTION    AND    THERMAL    MEASUREMENTS  IQ 

.sulated  from  the  stem  is  passed.  To  this  rod  the  post,  I,  is  at- 
tached, and  the  post,  H,  is  attached  to  the  stem.  Contact  with 
the  current  is  made  at  K  and  at  any  convenient  point  on  the 
.stem,  and  the  metallic  circuit  is  completed  by  the  small,  iron 
wire,  G.  The  current  burns  the  wire  and  thus  ignites  the  mix- 
ture. 

Calorific  Power  by  Calculation.  —  Knowing  the  calorific  powers 
of  the  several  elements  constituting  a  fuel,  its  heating  value  may 
be  calculated  from  the  results  of  a  chemical  analysis.  For  ex- 
ample: A  fuel  contains  80  per  cent,  carbon,  15  per  cent,  hydro- 
gen, and  5  per  cent,  sulphur.  Referring  to  the  table  (p.  23)  for  the 
elements  —  • 

0.80  (  8080)  +o.  1  5  (  34500)  +0.05  (  2220)  =  11  750  calories. 

If  the  fuel  contains  oxygen  already  combined  with  hydrogen, 
it  is  obvious  that  so  much  hydrogen  is  not  available  as  a  com- 
bustible ingredient,  and  should  be  deducted  from  the  total  hydro- 
gen in  calculating  the  calorific  power.  Since  oxygen  combines 
with  one-eighth  of  its  own  weight  of  hydrogen,  the  calorific 

power  of  hydrogen  becomes  ^H  ---  -j  34500. 

Calorific  Intensity.  —  By  calorific  intensity  is  meant  the  temper- 
ature to  which  the  products  of  combustion  will  be  raised  when  a 
fuel  is  burned  under  given  conditions.  The  highest  temperature 
is  attained  when  a  fuel  is  burned  in  a  ready  but  not  excessive 
supply  of  pure  oxygen.  The  calorific  intensity  is  found  by  divid- 
ing the  calorific  power  by  the  weight  of  the  products  of  com- 
bustion, multiplied  respectively  by  their  specific  heats,  thus: 


c    I     - 


_ 

+  W2S2  +  W3S3,  etc.  ' 

The  weights  of  the  several  products  are  represented  by  W1W.2 
W3,  etc.,  and  the  specific  heats  by  SjSoSg,  etc.  Engineers  use 
a  similar  expression  to  denote  the  evaporative  poiver  of  fuels. 
Numerically  expressed,  the  evaporative  power  is  the  weight  of 
water,  at.ioo0  C.,  that  a  unit  weight  of  a  fuel  will  convert  into 
steam.  It  is  found  by  dividing  the  calorific  power  by  537,  the 
latent  heat  of  steam. 

Pyrometry.  —  Laboratory  experiments  may  be  valuable  so  far 


2O  METALLURGY 

as  they  go,  but  the  actual  efficiency  of  fuels  can  not  be  deter- 
mined in  this  way.  No  more  should  be  expected  from  such  de- 
terminations than  the  relative  heating  values.  The  most  prac- 
tical results  are  gained  by  putting  the  fuels  into  actual  use  for 
a  reasonable  length  of  time,  and  measuring  their  efficiencies  by 
the  work  done  or  by  whatever  means  are  at  hand.  In  the  attain- 
ment of  high  temperatures,  which  is  necessary  in  many  metal- 
lurgical processes,  the  temperatures  are  indicated  by  means  of 
pyrometers  (high  temperature  thermometers).  These  instruments 
are  especially  useful  when  it  is  desirable  to  know  the  range  of 
temperature  over  a  considerable  length  of  time,  as  they  are  now 
designed  to  plot  the  temperature  automatically.  Such  records 
may  be  used  to  denote  efficiency  or  regularity  of  heating,  as  the 
case  requires. 

The  first  practical  pyrometer  appears  to  have  been  devised  by 
Wedgewood,  who  realized  the  need  of  determining  and  con- 
trolling the  temperature  of  his  kilns.  The  indicator  which  he 
used  depended  upon  the  contraction  of  clay  at  high  temperatures. 
A  number  of  pyrometers  have  since  been  invented,  making  use  of 
different  principles.  Some  of  the  instruments  that  have  had  more 
general  application  may  be  defined  as  follows: 

Fusion  Point  Pyrometer,  making  use  of  the  known  melting 
points  of  different  metals  or  other  substances. 

Metal  Expansion  Pyrometer. — An  instrument  which  measures 
the  expansion  of  a  single  metal  or  of  two  metals  acting  differen- 
tially at  different  temperatures. 

Specific  Heat  Pyrometer. — Heat  is  transferred  from  the  fur- 
nace to  be  tested  to  a  definite  weight  of  water  by  a  metal  of 
known  specific  heat.  The  temperature '  to  which  the  water  is 
raised,  which  is  a  function  of  the  temperature  of  the  furnace,  is 
determined  by  means  of  a  thermometer. 

Heat  Conduction  Pyrometer. — A  current  of  \vater  of  known 
temperature  flows  at  constant  rate  through  a  tube  placed  in  the 
furnace.  The  increase  in  temperature  is  proportional  to  the  tem- 
perature of  the  furnace. 

Air  Pyrometer. — This  comprises  several  different  instruments 
which  make  use  of  t'he  expansive  force  of  air  when  heated.  The 


COMBUSTION    AND   THERMAL    MEASUREMENTS  21 

air  is  contained  in  a  vessel  of  porcelain  or  metal,  which  is  placed 
in  the  temperature  to  be  tested. 

Optical  Pyrometer. — The  temperature  is  measured  by  the  pho- 
tometric effect  of  the  radiations  from  substances  heated  in  the 
temperature  to  be  determined.  Another  depends  upon  the  polar- 
ization and  refraction  of  light  from  the  heated  surface  by  means 
of  Nicol  prisms  and  plates.  One  of  the  prisms  is  rotated  and 
the  angle  of  rotation  is  measured  as  in  the  operation  of  the  polar- 
iscope. 

Electric  Resistance  Pyrometer. — This  instrument  is  the  inven- 
tion of  William  Siemens.  It  makes  use  of  the  increased  resist- 
ance of  a  platinum  wire  with  the  increase  of  temperature.  The 
current  from  a  battery  is  made  to  pass  in  a  divided  circuit 
through  wires  of  equal  resistance.  One  of  these  wires,  which  is 
platinum,  is  placed  in  the  temperature  to  be  determined.  The  in- 
creased resistance  causes  a  proportionally  stronger  current  to 
flow  through  the  other  wire.  A  suitable  electric  measuring  instru- 
ment is  used  as  an  indicator. 

Thermo-Hlectric  Pyrometer. — This  instrument  represents 
chiefly  the  work  of  Le  Chatelier,  who  introduced  the  platinum- 
rhodium  couple.  The  principle  made  use  of  is  that  electrical 
equilibrium  is  disturbed  when  two  different  metals  in  contact  are 
heated. 

The  Bristol  pyrometer  is  of  the  Le  Chatelier  type.  It  is 
adaptable  to  both  scientific  and  practical  use.  The  principle  of 
this  instrument  is  shown  in  Fig.  6.  The  thermo-couple  consists 
of  platinum  and  rhodium  alloy  wires  fused  together  at  the  end 
and  insulated  by  a  special  preparation  of  asbestos  and  corundum. 
Copper  wires,  leading  to  a  galvanometer,  are  attached  to  the 
couple  outside  of  the  furnace.  The  galvanometer  measures  the 
potential  of  the  current  that  is  set  up  when  the  couple  is  heated. 
A  compensator  is  used  to  offset  the  effect  of  variations  in  tem- 
perature outside  the  furnace,  on  the  "cold  end"  of  the  couple. 
The  compensator  consists  of  a  glass  bulb,  having  a  narrow  neck, 
containing  mercury.  A  platinum  resistance  wire  passes  through 
the  walls  of  the  neck  and  dips  downward  into  the  mercury. 
Changes  in  temperature  cause  a  rise  and  fall  of  the  mercury  in 
the  neck  of  the  bulb,  as  in  the  capillary  tube  of  a  thermometer. 


2.2 


METALLURGY 


This  regulates  the  resistance  by  short-circuiting  more  or  less  of 
the  wire  loop. 

Fig.  7  shows  the  complete  apparatus  for  indicating  and  record- 
ing furnace  temperatures.  Following  the  direction  of  the  lead 
wires  from  the  "fire  end"  of  the  couple,  shown  at  the  left,  the 
case  attached  to  the  wall  contains  the  switch,  by  which  the  cur- 
rent is  directed  either  to  the  indicator  or  the  recorder.  The  in- 
dicator is  directly  below  the  switch  box  and  the  recorder  is  to 
the  left.  The  indicator  is  a  very  sensitive,  dead  beat  galvanometer, 
calibrated  to  read  degrees  of  heat  directly.  The  recorder  is  a 
specially  constructed  galvanometer  in  which  the  indicating  needle 
is  extended  into  a  slender  arm,  which  is  bent  at  right  angle  near 


THERMO-ELECTRIC 


LEADS  TO  INDICATING  INSTRUMENT 

Fig.  6 — Showing  Principle  of  Bristol  Pyrometer. 

the  end  and  pointed.  Behind  the  recorder  arm  is  placed  a  circu- 
lar chart,  ruled  to  show  the  position  of  the  pointer  in  terms  of 
temperature  degrees.  The  chart  corresponds  to  the  face  of  a 
clock,  being  driven  by  a  clock  movement,  and  having  equal  spaces 
ruled  to  denote  the  time  at  which  the  temperature  is  indicated. 
The  chart  is  of  paper  and  has  a  sensitized,  smoked  surface.  The 
record  is  shown  as  a  continuous  line  by  vibrating  the  chart  at 
short  intervals  to  bring  the  sensitive  surface  in  contact  with  the 
point  of  the  needle.  The  vibration  is  effected  by  a  mechanism 
under  control  of  the  clock  movement. 


1 


COMBUSTION    AND    THERMAL    MEASUREMENTS  23 

CALORIFIC  EFFECT  OF  SOME  OXIDATION  REACTIONS.  l 

Element.  Product.  Calories. 


Hydrogen 

H20 

34,500 

Carbon 

C02 

8,080 

Silicon 

Si02 

7,720 

Phosphorus 

P205 

5,966 

Arsenic 

As203 

2,925 

Sulphur 

S02 

2,220 

Iron 

FesO, 

1,585 

Zinc 

ZnO 

1,321 

Copper 

Cu2O 

321 

Lead 

PbO 

239 

Mercury 

HgO 

no 

Nitrogen 

NO 

—i,54i 

1  Substantially  the  values  given  by  Thomsen. 


CHAPTER  IV 


CLASSIFICATION  AND  DESCRIPTION  OF  THE  FUELS- 
THE  NATURAL  FUELS 

The  three  physical  conditions  of  matter  are  represented  in  the 
fuels.  Practically  all  the  fuels  used  in  metallurgical  operations 
consist  of  some  kind  of  coal,  or  a  product  of  coal.  The  use  of 
liquid  and  gaseous  fuels  is  of  recent  origin,  but  it  has  grown 
rapidly.  Especially  is  this  true  of  gas,  which  is  now  produced 
economically  for  manufacturing  purposes. 

There  are  several  points  favoring  the  use  of  fluid  and  gaseous 
fuels.  On  account  of  the  ease  with  which  they  can  be  handled 
and  their  freedom  from  foreign  matter,  gases  can  be  burnt  with 
greatest  economy,  and  a  high  temperature  is  reached  in  a  mini- 
mum time;  the  heat  can  be  directed  to  the  locality  desired  and 
the  temperature  easily  controlled;  the  contents  of  the  furnace  are 
not  contaminated  with  foreign  matter,  and  there  is  no  ash  to  be 
disposed  of.  In  consequence  of  these  facts  greater  uniformity  of 
working  is  possible.  There  are,  however,  some  important  opera- 
tions requiring  fuel  in  the  solid  form,  and  the  relative  abundance 
and  low  cost  of  solid  fuels  maintains  for  them  first  place. 

The  industrial  fuels  embrace  quite  a  variety  of  substances. 
Some  of  these  are  used  in  their  natural  state  and  some  are  arti- 
ficially prepared.  In  the  classification  of  fuels  the  first  division  is, 
therefore,  suggested.  Representative  analyses  of  the  fuels  are 
given  on  page  45. 

THE  NATURAL  FUELS 

Wood. — Air  dried  wood  consists  mainly  of  cellulose 
(C6H10O5)  and  a  variable  amount  of  uncombined  water.  Its 
usage  as  a  fuel  continues  in  localities  where  forests  abound  and 
coal  is  dear.  The  heating  power  of  wood  is  low,  as  would  be 
inferred  from  its  composition.  Being  the  material  from  which 
charcoal  is  prepared,  wood  is  still  of  some  importance  to  metal- 
lurgical industries. 

Peat. — This  material,  though  of  but  slight  use  in  metallurgy, 


CLASSIFICATION    AND   DESCRIPTION    OF    FUELS  25 

is  interesting  from  a  scientific  standpoint  in  its  relation  to  the 
other  fossil  fuels.  Peat  is  formed  by  the  decomposition  of  vegeta- 
ble matter  without  free  access  of  air.  In  the  composition  of  plant 
tissues  carbon  is  the  nucleus  or  central  element  with  which  the 
other  elements,  chiefly  oxygen  and  hydrogen,  are  combined.  These 
elements  are  attached  to  the  carbon  by  feeble  chemical  bonds — a 
characteristic  of  carbon  compounds — and  in  the  decomposition  of 
plant  matter  under  peculiar  conditions  the  carbon  is  gradually 
isolated,  though  a  part  may  pass  off  in  combination  with  hydro- 
gen as  marsh  gas  (CH4),  and  a  part  in  combination  with  oxygen 
as  carbonic  acid  gas  (CO2).  The  localities  in  which  peat  forms 
are  swampy,  the  necessary  conditions  being  plant  growth  to  fur- 
nish the  carbonaceous  material ;  sufficient  warmth  to  promote  de- 
composition, and  the  presence  of  water,  which  covers  the  deposit 
and  prevents  complete  decomposition.  When  conditions  have 
been  favorable  this  process  has  gone  on  year  after  year,  each 
crop  being  deposited  on  the  remains  of  the  one  preceding,  until 
a  peat  bed  of  considerable  depth  has  been  formed.  The  gases 
mentioned  above  are  easily  detected  in  peaty  marshes,  and  the 
peat  bed  continues  to  grow  until  disturbed  by  natural  conditions 
or  by  man.  Large  deposits  of  peat  occur  in  Ireland,  and  in  less 
quantity  it  has  been  found  in  the  northeastern  part  of  the  United 
States. 

lit  is  readily  seen  from  its  composition  that  peat  is  a  poor 
fuel.  It  is  extremely  variable  in  composition,  the  carbon  varying 
from  50  to  60  per  cent,  in  dried  samples.  The  ash  may  be  as 
low  as  i  or  as  high  as  33  per  cent.,  due  to  the  admixture  of 
earthy  matter.  The  best  peat  is  found  at  the  bottom  of  the  bed, 
where  decomposition  has  proceeded  furthest.  In  the  surface  por- 
tion the  plant  roots  and  stems  can  be  seen.  Peat  is  too  bulky  to 
be  transported  profitably.  Its  value  is  greatly  increased  by  dry- 
ing and  pressing.  It  is  manufactured  for  domestic  use  into 
briquets  (compressed  blocks),  and  recently  it  has  been  converted 
into  charcoal. 

Lignite. — This  material  belongs  to  a  more  recent  geological 
period  than  the  true  coals.  In  composition  it  may  be  considered 


26  METALLURGY 

as  intermediate  between  peat  and  coal.  The  principle  deposits 
of  lignite  in  the  United  States  are  west  of  the  Mississippi  River. 

The  lignites  are  characterized  by  their  brownish  streak  and  lus- 
ter and  frequently  by  their  woody  (ligneous)  structure,  showing 
perfectly  the  grain  of  the  wood  from  which  they  are  formed. 
Whole  trunks  of  trees  are  sometimes  found  imbedded  in  lignite 
deposits.  Lignites  are  often  spoken  of  as  the  "brown  coals".  They 
are  quite  variable  in  composition,  and  are  comparatively  poor  fuels. 

Coal. — Modern  metallurgy  is  dependent  for  its  fuel  almost  en- 
tirely upon  coal,  or  varieties  of  fuel  derived  from  coal.  No  sub- 
stance has  been  mined  so  extensively  as  coal,  and  no  other  sub- 
stance is  the  source  of  so  many  and  varied  manufactured  products. 
There  is  still  much  that  is  not  understood  about  the  formation  of 
coal,  but  there  is  no  doubt  that  it  is  of  vegetable  origin,  represent- 
ing the  oldest  of  such  formations.  All  woody  or  fibrous  structure 
has  disappeared  in  the  true  coals,  and  in  some  varieties  the  carbon 
has  been  almost  completely  isolated.  Quite  a  good  deal  may  be 
learned  about  the  composition  and  properties  of  a  coal  by  a  simple 
determination.  This  is  conducted  as  follo\vs : 

A  certain  weight  of  the  coal  to  be  examined  is  put  into  a 
weighed  crucible.  After  covering  the  crucible  to  prevent  the  es- 
cape of  solid  particles,  it  is  heated  gradually  to  bright  redness, 
and  that  temperature  is  maintained  for  a  few  minutes,  after  which 
the  crucible  and  its  contents  are  cooled  and  again  weighed.  The 
volatile  matter,  or  loss  in  weight,  consists  partly  of  water,  but  it  is 
chiefly  hydrocarbon  gases  resulting  from  the  composition  of  the 
coal.  These  with  some  hydrogen  and  possibly  sulphur  constitute 
the  "  volatile  combustible  matter  "  of  coals.  The  residue  in  the 
crucible  consists  mainly  of  carbon  and  the  non-combustible  part  of 
the  coal,  or  the  ash.  If  the  volatile  matter  is  very  high,  the  residue 
will  have  fused  or  cemented  together  into  a  cake  of  some  firmness. 
If  the  coal  softens  and  swells  a  good  deal,  the  cake  is  left  light 
and  friable — characteristic  of  coals  high  in  volatile  combustible 
matter.  If  on  the  other  hand,  there  is  but  slight  softening  and  less 
volatile  matter,  the  cake  is  harder  and  firmer  and  more  difficult 
to  burn.  Such  a  residue  is  termed  a  true  coke.  The  experiment 
may  be  further  continued  by  removing  the  crucible  lid,  and  heat- 


CLASSIFICATION    AND    DESCRIPTION    OF    FUELS  2.J 

ing  externally  until  the  carbon  of  the  residue  is  entirely  consumed. 
The  residue  now  remaining  is  the  ash,  which  is  determined  directly 
by  weighing.  The  difference  between  the  sum  of  the  weights  of 
volatile  matter  and  ash,  and  the  weight  of  the  coal  is  called  "fixed 
carbon,"  a  term  which  is  practically  though  not  absolutely  correct, 
if  the  volatile  matter  is  very  low  the  residue  in  the  covered  cruci- 
ble will  appear  the  same  after  as  before  ignition. 

The  Coals  Classified. — The  fundamental  properties  of  a  coal 
may  be  learned  from  the  above  experiment,  and  also  its  fitness 
as  a  fuel  for  certain  operations.  For  industrial  purposes,  coals 
are  classified  according  to  their  behavior  during  combustion.  Some 
burn  with  and  some  without  flame,  the  former  usually  showing 
a  tendency  to  fuse  or  soften  when  heated.  In  general,  those 
coals  yielding  volatile  combustible  matter,  and  consequently  burn- 
ing with  a  flame  are  called  bituminous,  and  those  yielding  but 
little  volatile  matter  and  burning  with  practically  no  flame  are 
called  anthracite. 

Bituminous. — The  coals  of  this  class  vary  much  in  composition 
and  general  properties.  They  are  intermediate  between  the  lig- 
nites and  the  anthracites,  and  may  be  said  to  represent  every  stage 
of  transition  between  these  widely  differing  classes.  There  is,  how- 
ever, no  sharp  line  of  difference  between  lignite  and  true  coal, 
or  between  bituminous  coal  and  anthracite.  The  bituminous  coals 
are  characterized  by  their  black  or  brownish  color,  dull  luster 
cubical  or  conchoidal  fracture  and  the  ease  with  which  they  burn. 
They  are,  by  far,  the  most  abundant,  and  are  very  widely  dis- 
tributed. With  further  reference  to  their  manner  of  burning,  the 
bituminous  coals  are  divided  into  the  following  general  classes: 
Class  I.  Cannel  Coals— -This  class  differs  from  the  others 
in  several  particulars.  The  cannel  coals  burn  with  greatest  ease, 
many  varieties  can  be  kindled  with  a  match,  but  they  do  not  soften 
when  heated.  They  are  dense  in  structure,  black  with  a  dull 
luster,  and  do  not  soil  the  hands.  Cannel  coal  is  readily  distilled, 
and  yields  a  rich  illuminating  gas,  the  residue  containing  but 
little  combustible  matter.  The  percentage  of  ash  in  cannel  coal  is 
generally  high,  rendering  it  unfit  for  direct  firing. 

Class  2.     Long   Flame-Caking    Coals. — This    class    comprises 


28 


what  are  generally  known  as  the  soft  coals.  These  coals  resemble 
the  cannels  in  burning  with  a  long,  smoky  flame,  but  unlike  the 
cannels,  they  soften  and  swell  when  heated,  and  if  finely  divided, 
run  together  forming  a  pasty  or  tarry  mass.  The  volatile  matter 
distills  off  from  this,  leaving  a  light,  porous  coke.  If  the  coke  is 
dense  and  hard  it  indicates  that  a  large  amount  of  mineral  matter 
(ash)  is  present.  On  account  of  this  fusing  property  special 
methods  of  firing  are  employed,  where  clinkers  are  objectionable 
or  the  draft  would  be  shut  off.  The  long  flame  coals  are  much 
used  for  heating  boilers,  for  certain  types  of  furnaces  and  for 
making  gas. 

Class  j.  Short  Flame-Coking  Coals.  —  This  is  now  the  most 
important  class  of  coals  on  account  of  the  variety  of  industries 
it  affects.  It  embraces  all  varieties  of  coal  which  can  be  used  for 
making  metallurgical  coke.  The  typical  coals  of  this  class  burn 
with  a  short  flame,  yield  less  gas  than  the  other  bituminous  coals, 
and  they  soften  and  swell  but  little  when  burning.  When  burned 
under  proper  conditions  they  cement  together,  forming  a  dense, 
hard  coke  of  high  calorific  power.  The  best  varieties  yield  about 
80  per  cent,  of  coke.  These  coals  are  largely  used  for  raising 
steam,  but  their  chief  use  is  in  coke  making.  They  will  be  further 
studied  under  this  subject.  There  are  a  number  of  varieties  in- 
termediate between  the  coking  coals  and  anthracite. 

Anthracite.  —  The  anthracites  represent  the  oldest  of  all  the  coal 
formations.  They  are  found  in  many  parts  of  the  world,  but  in 
comparatively  small  quantities.  The  largest  known  deposits  are 
those  of  Eastern-central  Pennsylvania.  The  characteristic  proper- 
ties of  true  anthracite  are  superior  hardness  to  all  other  coals, 
submetallic  luster  and  density  of  structure.  It  rings  when  struck 
and  soils  the  hands  but  little.  When  burnt  in  a  plentiful  supply 
of  air,  anthracite  gives  little  or  no  flame,  being  practically  free 
from  volatile  gases.  It  shows  no  tendency  to  soften  in  the  fire, 
and  is  difficult  to  kindle.  Anthracite  is  not  much  used  in  metal- 
lurgy except  as  a  reducing  agent  where  coke  would  not  answer. 
It  is  the  favorite  domestic  coal,  and  is  used  quite  extensively  for 
heating  boilers,  especially  locomotive  boilers. 

Natural  Gas.  —  The  chief  component  of  this  remarkable  fuel  is 


CLASSIFICATION    AND    DESCRIPTION    OF   FUELS  29 

marsh  gas,  the  same  substance  that  is  formed  by  the  decomposi- 
tion of  vegetable  matter  in  peat  formations,  and  is  always  found 
in  soft  coal  and  oil  measures.  The  presence  of  natural  gas, 
which  is  always  associated  with  petroleum,  is  due  part- 
ly to  the  retaining  properties  of  the  rock  in  which  it 
occurs.  It  is  found  in  porous  limestone  and  sandstone, 
usually  under  great  pressure.  The  only  large  deposits  of 
natnral  #as  known  are  in  the  United  States.  It  was  discovered  at 
a  few  points  more  than  a  hundred  years  ago,  the  first  recorded  use 
of  it  being  at  Hredonia,  N.  Y.  (1821),  where  it  was  used  for  light- 
ing purposes.  It  was  discovered  in  Western  Pennsylvania  by  oil 
prospectors,  and  this  led  to  the  opening  of  the  immense  reservoirs 
in  Ohio,  Indiana  and  West  Virginia.  It  was  the  common  belief 
for  a  while  that  the  gas  deposits  were  inexhaustible,  and  large 
quantities  of  this  valuable  material  were  wasted,  there  being  no 
immediate  use  for  it.  It  is  said  that  up  to  the  year  1895  more  gas 
was  allowed  to  waste  than  was  actually  used.  The  idea  of  piping 
it  to  the  distant  cities  and  manufactories  had  not  occurred  to  the 
oil  seekers.  Wells  were  drilled  into  the  gas-bearing  rock,  and 
after  allowing  all  the  gas  in  that  vicinity  to  escape,  the  wells  were 
sunk  deeper  for  the  oil.  When  it  was  found  that  the  supply  of 
this  ready  made  fuel  was  becoming  exhausted,  further  steps  were 
taken  to  utilize  it,  and  the  price  began  to  advance.  The  gas  is 
led  through  pipes  from  West  Virginia  wells  to  Pittsburg  and 
neighboring  towns,  a  distance  of  more  than  100  miles.  In  addi- 
tion to  this,  other  lines  have  been  laid,  some  extending  into  Oliio, 
where  the  supply  has  been  largely  exhausted.  The  latest  important 
•discoveries  of  gas  have  been  made  in  Kansas.  It  is  impossible  to 
tell  how  long  natural  gas  will  last,  even  if  the  rate  of  consumption 
were  known,  but  it  will  probably  not  be  used  many  more  years  in 
the  metallurgical  industries. 

The  principle  application  of  natural  gas  to  metallurgical  pro- 
cesses is  in  the  open  hearth  process  of  steel  making,  and  in  reheat- 
ing furnaces. 


CHAPTER   V 


THE  PREPARED  FUELS 

The  artificial  or  prepared  fuels,  as  described  in  this  text,  are 
those  which  have  been  chemically  altered  from  their  natural 
state.  They  are  prepared  almost  exclusively  from  coal  and  wood, 
and,  practically  speaking,  are  either  solids  or  gases.  Mention, 
however,  is  made  of  the  fuels  derived  from  petroleum,  whose 
future  use  is  uncertain. 

The  principles  made  use  of  in  the  manufacture  of  fuels  are  de- 
structive distillation  and  partial  combustion  of  the  natural  mate- 
rial. Processes  involving  destructive  distillation  are  common  in 
chemical  industries.  By  the  term  is  meant  the  heating  of  any 
compound  without  access  of  air,  until  it  is  decomposed,  and  the 
volatile  constituents  are  driven  oft.  In  the  destructive  distillation 
of  fuel  materials,  the  products  are  compound  gases,  tarry  matter,, 
water  holding  various  substances  in  solution,  and  a  residue  of 
carbon  with  varying  amounts  of  impurities.  The  residue  is  usual- 
ly the  product  aimed  at,  while  the  others  (the  by-products)  may 
be  utilized,  though  they  are  often  allowed  to  waste. 

Charcoal. — When  wood  is  distilled  the  hydrogen  and  oxygen 
pass  off  mainly  as  water.  A  small  portion  of  the  carbon  also 
passes  off  in  combination  with  these  elements,  while  the  greater 
part  remains  behind  in  a  practically  pure  form,  as  charcoal.  The 
preparation  of  charcoal  was  engaged  in  by  the  ancients,  and  is 
still  an  important  industry,  though  the  use  of  this  fuel  in  metal- 
lurgy has  been  almost  abandoned.  There  are,  however,  even  in 
civilized  countries,  districts  that  are  heavily  wooded  and  without 
coal,  in  which  large  amounts  of  charcoal  are  made  and  used.  The 
composition  and  quality  of  charcoal  depends  upon  the  kind  of 
wood  from  which  it  is  made  and  the  manner  in  which  it  is  pre- 
pared. Mature  woods  of  slow  growth  are  the  best,  and  the  char- 
.ring  should  be  done  slowly  and  until  the  fixed  carbon  begins  to 
burn.  From  this  it  is  seen  that  the  best  charcoal  is  not  made  by 
purely  distillation  processes.  Good  charcoal  retains  the  structure 


THE    PREPARED    FUELS  31 

of  the  wood,  showing  the  pores  and  rings  of  annual  growth.  It 
should  be  firm,  and  should  burn  without  flame  in  a  plentiful  sup- 
ply of  air.  It  is  an  indication  of  good  quality  if  it  rings  when 
struck.  Charcoal  has  a  remarkable  absorbent  power,  taking  up 
many  times  its  own  volume  of  a  gas,  or  a  quantity  of  water.  For 
this  reason  its  usefulness  as  a  fuel  is  greatly  impaired  by  exposure 
to  the  weather. 

Charcoal  is  a  by-product  in  the  manufacture  of  acetic  acid  and 
methyl  alcohol.  This  is  of  an  inferior  grade,  as  the  wood  is 
•distilled  from  retorts  that  are  heated  externally,  and  to  which  no 
air  is  admitted.  The  result  of  this  is  that  no  combustion  takes 
place,  and  the  residue  is  not  completely  charred.  The  charring 
is  most  complete  when  the  volatile  combustible  matter  is  burned 
in  contact  with  the  wood,  no  external  heat  being  used.  In  local- 
ities where  large  quantities  of  charcoal  are  used,  it  is  made  in  heaps 
covered  with  turf,  or  in  ovens,  constructed  so  that  the  proper 
amount  of  air  can  be  admitted.  The  wood  for  charcoal  burning 


Fig.  8. 

.should  be  felled  in  winter,  while  it  contains  the  least  sap,  and  al- 
lowed to  season  until  late  in  the  following  summer.  If  kept  long- 
er the  wood  might  become  too  dry,  and  loss  would  occur  in  burn- 
ing. The  bark  is  sometimes  stripped  off,  as  it  contains  phos- 
phorus, and  makes  inferior  charcoal. 

Figure  8  shows  the  arrangement  of  a  charcoal  heap  or  mound. 
One  half  of  the  drawing  is  a  section  through  the  interior,  show- 
ing the  arrangement  of  the  wood.  The  heap  is  built  upon  a 
-circular  foundation  of  earth,  which  is  trenched  around  for  drain- 
age. The  diameter  of  the  heap  at  the  base  is  about  40  feet, 
and  it  contains  four  courses  of  wood  cut  in  4  foot  lengths  and  set 
on  end.  The  wood  is  set  around  a  central,  triangular  flue,  the 


32  METALLURGY 

small  and  crooked  pieces  being  placed  on  the  exterior.  The  fin- 
ished heap  is  covered  with  leaves,  and  upon  these  7  inches  of  earth 
is  thrown.  The  top  of  the  flue  is  left  open  for  firing  the  heap, 
and  openings  are  made  at  intervals  around  the  base  to  admit  air. 
The  heap  is  kindled  by  dropping  fire  brands  down  the  central 
flue  and  filling  it  with  dry  wood.  The  opening  at  the  top  is  then 
closed,  and  the  fire  is  left  to  smolder.  At  the  end  of  two  weeks 
the  charring  is  well  under  way.  The  process  is  now  hastened  by 
opening  a  row  of  small  holes  around  the  mound  at  a  distance  of 
2  to  3  feet  from  the  ground  line.  The  wood  in  the  upper  and 
central  portion  of  the  heap  is  the  first  to  be  converted  into  char- 
coal, and  the  charring  proceeds  downward  and  outward.  The 
collier  packs  the  earth  down  upon  the  heap,  and  carefully  avoids 
any  access  of  air  in  the  upper  part.  As  the  fire  approaches  the 
circle  of  small  flu^s  the  smoke  issuing  therefrom  becomes  blue  and 
hot,  all  water  vapor  having  disappeared.  The  flues  are  closed  and 
another  lot  is  made  further  down.  When  the  fire  reaches  the 
second  line  of  flues  the  process  is  completed.  The  time  required 
is  18  to  21  days.  A  heap  of  the  above  dimensions  should  yield 
upwards  of  2,000  bushels  of  charcoal. 

Coke. — Coke  was  first  manufactured  and  used  by  Dud  Dudley, 
an  English  iron  master,  in  the  early  part  of  the  I7th  century.1 
The  peculiar  condition  of  affairs  in  England  at  that  time  did  not 
permit  Dudley  to  reap  the  fruits  of  his  invention,  and  his  enter- 
prise had  to  be  abandoned.  It  was  almost  a  hundred  years  before 
coke  making  was  resumed.  Its  superiority  over  coal  as  a  blast- 
furnace fuel  once  fully  appreciated,  coke  was  soon  made  on  the 
large  scale.  The  original  process  consisted  in  smoldering  a 
heap  of  coal  under  a  cover  of  earth  or  cinders,  the  product  being 
irregular  in  quality  and  the  yield  low.  Coke  was  first  manufac- 
tured in  the  interest  of  the  iron  industry,  which  industry  has  con- 
tinued to  be  its  chief  consumer. 

The  characteristics  of  good  coke  are  firmness,  light  color  and 
luster,  and  freedom  from  dark  spots.  The  ash  should 

1  A  reprint  of  Dudley's  interesting  paper  "  Metallum  Martis  "  appeared 
in  Jour.  Iron  and  Steel  Inst.,  1872,  2,  215. 


THE     PREPARED 

be  as  low  as  possible  and  there  should  be  minimum 
amounts  of  sulphur  and  phosphorus  present.  In  the  dis- 
tillation of  coal  the  volatile  products  consist  of  the  hydrocar- 
bons and  other  gases,  ammonia  and  tar.  The  composition  of 
coal  gas  is  given  in  the  fuel  table.  The  present  processes  of 
coke  manufacture  employ  three  distinct  methods  for  disposing 
of  the  volatile  products,  or  as  they  are  known,  the  by-products. 
Hence  there  are  three  distinct  types  of  oven.  In  the  ovens  of  the 
first  type  the  by-products  are  consumed  for  the  most  part  in  the 
oven,  and  in  contact  with  the  solid  matter,  the  combustion  being 
finished  at  the  mouth  of  the  oven.  A  small  amount  of  air  is 
necessarily  admitted  into  the  oven  to  accomplish  this  result.  The 
ovens  of  the  second  class  do  not  admit  air,  but  the  by-products 


Fig.  9. 

are  distilled  off  and  burned  underneath  or  at  the  sides  of  the  oven, 
furnishing  the  necessary  amount  of  heat  to  carry  on  the  distilla- 
tion. The  third  class  of  ovens  makes  use  of  the  initial  heat  of  the 
by-products  for  the  distillation,  but  recovers  the  larger  part  of 
them  for  other  purposes. 

/.  The  Beehive  Oven. — The  form  of  this  oven  suggests  the 
name.  The  section  of  a  beehive  oven  is  shown  in  Fig.  9.  It  is  a 
hemispherical  enclosure,  lined  with  fire-brick,  the  outer  walls  be- 
ing built  of  rough  stone  or  other  cheap  material.  The  circular  open- 
ing at  the  top  is  for  introducing  the  charge,  and  is  the  flue  from 
which  the  products  of  combustion  and  distillation  escape.  The 
opening  at  the  side  and  base  is  for  withdrawing  the  coke.  Fig.  10 


34 


METALLURGY 


shows  the  general  arrangement  of  the  ovens.  These  are  called 
"bank"  ovens.  They  are  also  built  in  double  rows,  and  are  then 
known  as  "block"  ovens.  The  bank  ovens  are  cheaper  to  con- 
struct, but  the  block  ovens  can  be  operated  more  economically. 
A  railway  traverses  the  system,  and  over  this  the  larry  with  coai 
for  the  ovens  is  driven.  The  larry  is  generally  operated  by  elec- 
tricity. The  space  in  front  of  the  ovens  is  the  coke  yard,  and 
below  this  is  a  standard  gage  track  for  the  coke  cars.  The  ovens 
are  built  as  near  the  coal  mines  as  practicable,  so  as  to  save 
transportation  costs. 

Coke  burning  in  beehive  ovens  is  a  simple  operation  and  re- 


Fig.  10. 

quires  no  skilled  labor.  The  crushed  coal,  or  slack  is  charged 
and  kindled,  enough  heat  remaining  after  each  charge  is  with- 
drawn to  kindle  the  next.  The  door  at  the  side  is  closed  with 
the  exception  of  a  small  opening  to  admit  the  necessary  amount 
of  air.  The  temperature  rises  slowly,  and  after  a  few  hours  a 
flame  appears  at  the  mouth  of  the  oven.  Heat  is  reflected  upon 
the  mass  from  the  dome-shaped  lining,  and  it  becomes  glowing 
hot  after  most  of  the  volatile  matter  has  been  driven  off.  Com- 
bustion may  be  said  to  begin  at  the  top  and  proceed  downwards. 
In  an  oven  taking  a  charge  of  3  tons  of  coal,  the  time  required 
for  driving  off  the  volatile  matter  is  about  48  hours.  The  coke 
may  be  taken  at  this  stage,  but  it  is  usually  allowed  to  remain  in 
the  oven  for  60  hours  from  the  time  of  charging.  During  the 
last  12  hours  the  side-door  is  closed  completely,  while  the  coke 
remains  at  a  bright  red  heat.  Water  is  now  introduced  into  the 


THE:  PREPARED  FUELS  35 

oven  at  the  top,  by  means  of  a  hose,  until  the  coke  is  cool  enough 
to  handle.  The  coke  is  raked  out  through  the  side-door  by  labor- 
ers. Mechanical  drawers  have  been  installed  at  some  of  the  large 
plants.1 

2.  Ovens  Excluding  Air  and  Burning  the  By-Products. — While 
the  beehive  oven  is  cheapest  to  build  and  to  operate,  there  is  a 
tremendous  waste  of  heat  sustained,  and  by  the  admission  of  air 
into  the  oven  some  of  the  coke  itself  is  burned.  These  losses  have 
been  greatly  lessened  by  excluding  the  air  from  the  coking  cham- 
ber, making  the  process  entirely  one  of  distillation.  The  neces- 
sary heat  is  derived  from  burning  the  products  of  distillation  un- 
derneath and  at  the  sides  of  the  chamber.  The  Copee  oven  may 
be  taken  as  a  representative  of  this  class.  It  differs  entirely  from 
the  beehive  oven,  the  interior  being  rectangular  and  measuring 
30  feet  in  length,  1%  feet  in  width  and  4  feet  in  height. 
The  roof  is  arched,  and  through  this  three  openings  with 
hoppers  are  provided  for  introducing  the  charges.  A  number  of 
these  ovens  are  built  in  series  with  the  longer  axes  parallel.  About 
30  vertical  flues  are  built  in  each  wall  common  to  two  ovens.  These 
open  into  the  ovens  and  into  horizontal  flues  situated  under  the 
ovens  and  running  their  entire  length.  Small  ports  open  into  the 
flues  from  the  top  to  admit  air. 

An  oven  being  hot  from  previous  running,  receives  a  charge  of 
fine  coal,  and  the  ends  of  the  chamber  are  closed  with  iron  doors. 
The  distillation  begins  at  once,  and  the  gases  pass  into  the  vertical 
flues  where  they  are  mixed  with  air  and  ignited.  From  these 
they  are  conducted  into  the  horizontal  flues  where  the  combustion 
is  completed.  The. heat  generated  by  the  burning  of  these  gases 
is  transmitted  to  the  coking  chamber.  The  ovens  are  worked  in 
pairs,  the  one  being  charged  when  the  distillation  in  the  other  is 
half  done.  The  supply  of  gas  is  kept  up  in  this  way. 

The  Appolt  oven  is  operated  on  the  same  principle  as  the  Copee, 
but  the  coking  chamber  differs  in  shape  and  size,  and  the  oven  is 
built  with  the  longest  dimension  vertical,  instead  of  horizontal. 

j.  Ovens  Excluding  Air  and  Recovering  By-Products. — It  was 
seen  from  the  description  of  the  Copee  oven  that  the  by-products 

1  A  plant  of  this  sort  at  Latrobe,  Pa.,  has  been  described  with  illustra- 
tions in  Trans.  Am.  Inst.  of  Min.  Eng.,  26,  346. 


30  METALLURGY 

are  not  made  use  of  except  in  connection  with  the  coking  process. 
The  heat  needed  for  distilling  a  coking  coal  is  far  less  than  that 
produced  by  burning  the  volatile  products.  In  recognition  of  this 
fact  the  "by-product"  oven  has  been  designed  to  reserve  a  part 
of  the  volatile  matter,  to  be  used  for  other  purposes.  This  is  ac- 
complished by  utilizing  the  initial  heat  of  the  gases  as  they  come 
from  the  oven,  and  burning  as  much  as  is  necessary  to  keep  up 
the  temperature  of  distillation.  Of  the  by-product  ovens  now 
in  use,  the  Otto-Hoffman  is  the  most  prominent.  This  oven  has 
itself  undergone  changes  in  the  details  of  its  construction,  some 
important  improvements  having  been  introduced  for  handling 
material  and  saving  labor  generally.  It  is  of  German  origin, 
being  the  improved  form  of  one  designed  by  C.  Otto,  of  Ger- 
many. 


Fig.  it. 

Figure  n  represents  a  type  of  Otto-Hoffman  oven.  The  sec- 
tion to  the  left  of  the  line  AB  is  through  an  oven  chamber,  and  the 
section  to  the  right  is  through  the  wall  between  two  ovens.  The 
ovens  are  supported  on  arches  of  masonry,  and  the  superstruc- 
ture is  reinforced  with  beams  and  tie-rods.  Three  larries  trav- 
erse the  system  on  top  to  supply  coal  to  the  ovens.  The  openings 
for  introducing  the  coal  are  shown  in  the  section  to  the  left  of  the 
line  AB.  The  opening  to  the  extreme  left  serves  for  the  passage 
of  gas  from  the  oven,  from  which  it  is  conducted  into  the  main, 
shown  in  cross-section.  The  coke  is  pushed  out  of  the  ovens  by 
means  of  a  ram,  which  is  shown  at  the  left.  This  machine  trav- 
erses the  entire  system  of  ovens  at  right  angles  to  their  axes.  It 
carries  a  long  beam  or  plunger  with  a  head  corresponding  in  shape 


THE     PREPARED    FUELS  37 

to  the  cross-section  of  an  oven,  and  an  engine  for  driving  the  beam 
to  and  fro.  With  this  device  an  oven  is  quickly  emptied  of  its 
charge,  and  the  coke  is  quenched  entirely  outside. 

In  heating  these  ovens,  the  so  called  regenerative  principle  is 
employed.  The  arched  chambers,  shown  in  cross-section 
at  the  right  and  left  of  the  foundation,  are  filled  with 
checker-work  of  fire-brick.  This  admits  of  the  free  pas- 
sage of  gases  through  the  chambers,  and  exposes  a 
very  large  surface  for  the  heating  or  cooling  of  the  brick  work 
as  the  case  may  be.  The  waste  products  of  combustion  are  led 
through  one  of  these  regenerators  until  the  brick  work  is  heated 
to  their  own  temperature.  The  air  for  the  combustion  is  heated 
by  passing  it  through  the  opposite  regenerator,  which  has  already 
been  heated.  By  means  of  reversing  valves,  the  hot  gases  and 
the  air  are  alternated  in  their  courses  so  that  one  of  the  regenera- 
tors is  being  heated  while  the  other  is  heating  the  air.  With  this 
saving  of  waste  heat,  the  amount  of  gas  needed  for  heating  the 
ovens  is  much  lessened.  The  combustion  takes  place  in  a 
chamber  beneath  the  division  walls,  the  gas  being  admitted  alter- 
nately from  burners  at  the  ends  of  the  ovens,  and  air  from  the 
regenerators.  The  products  of  combustion  are  directed  upward 
through  the  vertical  flues  in  one  half  of  the  partition  wall,  then 
through  the  horizontal  flue  above  the  oven  and  downward  through 
the  vertical  flues  in  the  other  half  of  the  partition  wall.  The  heat 
passes  through  the  thin  walls  of  fire-brick  and  distills  the  coal. 
After  surrounding  the  ovens  the  products  of  combustion  are  led 
through  the  regenerators,  and  finally  into  the  main  flue  communi- 
cating with  the  stack. 

The  gas  from  the  coking  chambers  is  cooled  to  recover  tar, 
and  then  passed  through  scrubbers  which  recover  ammonia.  The 
purified  gas  is  suitable  for  illuminating  purposes. 

Important  improvements  are  being  introduced  every  year 
bringing  about  greater  economy  in  operation  or  higher  yield, 
and  in  some  instances  a  better  quality  of  product.  Some  of  the 
most  notable  improvements  have  been  in  the  introduction  of  coke 
quenching  machines. 


3  METALLURGY 

Coke  Quenching  Machines. — These  machines  are  designed  to 
quench  a  charge  of  coke  without  exposing  it  to  the  air  and  with- 
out breaking  the  mass  to  pieces  as  it  is  drawn  from  the  oven. 
The  quenching  machine  is  essentially  a  closed  car  built  of  cast 
iron  plates  and  moves  on  a  track  at  right  angles  to  the  axes  of 
the  ovens.  It  is  of  sufficient  capacity  to  hold  the  entire  charge 
from  an  oven,  and  is  provided  with  the  necessary  apparatus  for 
spraying  the  coke  and  discharging  it  when  it  is  quenched.  The 
water  is  delivered  to  the  coke  through  nozzles  inside  the  car. 
The  coke  is  pushed  into  the  car  by  means  of  a  ram,  and  is 
quenched  by  the  water  and  steam,  the  conditions  being  some- 
what the  same  as  in  the  beehive  oven,  in  which  the  coke  is 
quenched  by  running  in  the  water  from  the  top.  The  coke  is 
discharged  mechanically  into  freight  cars,  thus  doing  away  en- 
tirely with  manual  labor. 

Desulphurization  of  Coke. — All  grades  of  coke  contain  some 
sulphur,  a  very  objectionable  ingredient  in  any  fuel  to  be  used  for 
smelting  iron.  The  sulphur  exists  in  the  coal  principally  as 
pyrite  (FeS2),  and  is  largely,  though  not  completely,  evolved 
in  the  process  of  coking.  Various  attempts  have  been  made  to 
remove  this  remaining  sulphur  from  coke,  but  no  process  has 
proved  satisfactory  for  general  use.  One,  however,  that  is  worthy 
of  notice  consists  in  passing  steam  through  a  heated  mass  of 
coke  to  decompose  sulphides  and  convert  the  sulphur  into  a  vol- 
atile form,  thus: 

Fe2S3+3H20=Fe203+3H2S. 

The  difficulties  here  met  with  are  due  to  the  fact  that  carbon 
decomposes  water  at  high  temperature,  entailing  a  loss  of  coke 
and  disintegration  of  the  lumps,  and  to  the  failure  of  the  steam, 
to  permeate  the  coke  mass  thoroughly. 

Theoretical  Considerations  and  Present  Status  of  Coke  Manu- 
facture.— The  quality  of  coke  depends  largely  upon  the  quality 
of  coal  from  which  it  is  manufactured.  If  the  coal  is  too  hard, 
inclining  to  anthracite,  it  will  not  soften  in  the  oven  sufficiently 
to  produce  a  coherent  coke.  If,  on  the  other  hand,  the  coal  is  too 
soft,  the  coke  will  be  light,  friable  and  of  low  heating  value. 
Coke  may  be  prepared  from  the  harder  coals  by  first  mixing 


THE    PREPARED    FUELS 


39 


them,  after  crushing,  with  soft  coal  or  any  material  yielding 
much  tar,  and  pressing.  A  process  is  now  in  use  for  making 
firmer  and  more  compact  coke  from  the  softer  coals,  which  con- 
sists in  ramming  or  packing  the  coal  as  it  is  charged  into  the 
oven. 

C.  G.  Atwater,  in  his  paper  on  " Development  of  the  Modern 
By-product  Coke  Oven,*'1  gives  some  interesting  data  on  the  pro- 
gress of  coking  in  the  Otto-Hoffman  oven.  The  diagram  (Fig. 
12),  taken  from  his  paper,  shows  the  progressive  temperatures 
in  different  parts  of  the  oven.  The  drawing  at  the  right  repre- 
sents the  door  of  the  oven,  and  the  small  circles  the  points  at 
which  the  holes  were  bored  for  taking  the  temperatures.  The 


0 


Fig.  u. 

numbers  correspond  with  the  numbers  of  the  lines  in  the  diagram. 
This  experiment  shows  that  the  distillation  begins  in  that  portion 
of  the  charge  lying  next  to  the  oven  walls,  and  proceeds  toward 
the  centre  of  the  mass.  The  gases  passing  from  the  interior,  on 
coming  in  contact  with  the  hotter  coke,  deposit  carbon,  thus  in 
a  measure  accounting  for  the  increase  in  yield  over  the  beehive! 
oven.  • 

The  economical  operation  of  by-product  ovens  is  largely  offset 
by  their  high  initial  cost.  As  coke  producers  for  blast  furnaces, 
they  have  been  made  to  compete  with  the  beehive  ovens  in  this 
country.  It  is  the  common  belief  that  by-product  coke  is  inferior 
to  that  produced  in  beehive  ovens  for  blast  furnace  work,  but 
this  has  not  been  conclusively  proved.  The  production  of  by- 
product coke,  both  for  domestic  and  industrial  uses,  is  yearly  in- 
creasing. The  statistics  below  have  their  significance. 
1  Trans.  Amer.  Inst.  Min.  Eng.,  33,  760. 


METALLURGY 


Figures  showing  the  percentage  of  the  total  production  of 
coke  that  has  been  produced  each  year  in  by-product  ovens  since 
1893,  the  year  they  were  introduced:1 

1893  1894  1895  1896  1897  1898  1899  1900  1901  1902  1903  1904  1905  1906 
0.13  0.18  0.14  0.7  2.0  1.8  4.6  5.35   5.4  5-5  7-4  n.i  io-7  ^5  9 

Producer  Gas. — No  fixed  composition  can  be  assigned  to  a  gas 
of  this  name,  though  the  analysis  given  at  the  end  of  the  chapter 


Fig-  13- 

is   typical.     It   consists   essentially   of   carbon   monoxide   mixed 
with  a  large  amount  of  nitrogen.     For  this  reason  its  calori- 
fic power  is  low.     It  is  almost  odorless  when  pure  and  is  poison- 
ous.    It  is  generally  enriched  with  water  gas  and  hydrocarbons. 
Almost  any  kind  of  solid  fuel  may  be  used  in  the  preparation 
of  producer  gas,  on  the  principle  that  carbon,  in  a  limited  supply 
1  C.  G.  Atwater,  in  the  Mineral  Industry. 


i^w^Tw^£fe^f  ~^ 

ipOT$£4*   / 


Fig.  14— Morgan,  Continuous  Gas  Producer  with  George,  Automatic  Feed. 
(Morgan  Construction  Co.) 


THE    PREPARED    FUELS  4! 

of  oxygen,  burns  to  carbon  monoxide.  This  is  probably  most 
accurately  expressed  as  follows: 

C+O2=:CO2,  and  CO2+C=2CO. 

The  necessary  conditions  for  the  above  reactions  are  sufficient 
heat  for  the  dissociation  of  carbon  dioxide  in  the  presence  of  a 
large  excess  of  carbon,  above  the  amount  actually  needed  for  the 
reduction.  The  blue  flame  often  seen  playing  over  a  grate  of  coals 
is  due  to  carbon  monoxide,  which  results  from  clogging  of  the 
draft.  The  gas  producer,  omitting  details  of  construction,  is 
nothing  more  than  a  deep  bed  of  coals  to  which  the  supply  of 
air  for  combustion  is  regulated.  The  original  producer,  as  de- 
signed by  Siemens,  is  represented  in  Fig  13.  The  coal  is  fed  in 
at  the  hopper,  H,  the  space  over  the  grate  bars,  B,  being  kept 
about  two-thirds  full.  The  gas  in  passing  up  from  the  fuel  bed 
enters  the  flue,  F,  through  which  it  is  conducted  into  the  gas 
main,  GM.  The  openings,  OO,  are  for  introducing  bars  to  stir 
the  fire  and  break  up  the  clinkers.  Water  is  kept  in  the  ash  pit 
under  the  grate.  The  vapor  from  this  enters  the  fire  bed,  where 
it  is  decomposed.  The  presence  of  steam  in  the  producer  pre- 
vents, to  a  large  extent,  the  formation  of  clinkers.  Steam  also 
enriches  the  gas,  as  will  be  shown  later. 

Fig.  14  represents  the  Morgan  producer,  with  automatic 
charging  apparatus.  The  producer  is  constructed  of  fire-brick 
encased  in  iron  plates.  It  is  cylindrical  in  shape  and  contracted 
toward  the  bottom.  No  grate  is  used,  but  the  ashes  are  re- 
ceived in  a  pan  of  water,  which  serves  to  cool  them  and  to  seal 
the  bottom  of  the  producer  from  the  air.  Air  is  supplied  to  the 
producer  through  a  central  pipe  terminating  near  the  bottom.  The 
pipe  is  provided  with  a  cap  for  distributing  the  blast.  Steam  is 
supplied  with  the  blast,  the  supply  being  regulated  by  means  of 
a  valve.  The  automatic  feeding  device  is  a  special  feature  of 
this  producer.  The  coal  is  fed  in  continuously  from  the  hopper, 
and  a  slowly  rotating,  inclined  spout  distributes  it  evenly  over 
the  surface  of  the  fuel  bed.  The  spout  and  top  of  the  producer 
are  water-cooled. 

The  water-sealed  type  of  producer  is  now  in  most  common 
use.  The  Taylor  producer  is  an  important  exception.  This  is 


42  METALLURGY 

provided  with  a  revolving  bottom,  and  the  fuel  is  supported  on 
a  deep  bed  of  ashes.  In  connection  with  some  gas  producer 
plants,  accessory  apparatus  is  employed  for  the  recovery  of  tar. 

The  manufacture  of  producer  gas  is  now  associated  with  many 
important  industries.  The  advantages  gained  in  the  use  of  gas 
as  fuel  have  been  fully  demonstrated,  and  it  has  been  left  to 
modern  invention  to  prepare  it  economically  and  in  large  quan- 
tities. City  gas,  which  was  formerly  prepared  entirely  by  the 
distillation  of  coal,  is  now  usually  prepared  by  enriching  pro- 
ducer gas  with  hydrocarbons  obtained  from  petroleum.  .The 
producer  is  advantageous  as  a  means  of  converting  a  poor  fuel 
into  gas.  Inferior  coal,  lignite,  peat  and  wood  may  be  thus  trans- 
formed into  an  excellent  fuel  for  industrial  purposes. 

Before  leaving  this  important  subject  it  will  be  well  to  note 
the  efficiency  which  might  be  expected  of  a  good  gas  producer. 
How  much  heating  value,  theoretical  and  actual,  is  lost  in  the 
conversion  of  solid  fuel  into  gas?  The  calorific  power  of  carbon 
is  the  total  heat  generated  when  it  is  burned  to  carbon  dioxide, 
or  8080  calories.  The  amount  of  heat  generated  when  it  is  burned 
to  carbon  monoxide  is  2416  calories,  leaving  5664  calories  to  be 
evolved  in  the  combustion  of  carbon  monoxide. 

If  all  the  heat  generated  in  the  producer  could  be  transferred 
to  the  combustion  chamber  of  the  furnace,  the  efficiency  of  the 
conversion  would  obviously  be  100  per  cent.  Losses  occur  from 
radiation  and  leakage  through  the  walls  of  the  producer  and  the 
gas  conduit,  from  the  heat  rendered  latent  in  the  formation  and 
expansion  of  gases  and  from  other  sources  unaccounted  for.  A 
large  amount  of  the  heat  of  combustion  in  the  producer  (C+O 
=CO)  may  be  saved  mechanically  by  using  insulating  material 
to  retard  radiation,  or  by  heating  the  air  supplied  to  the  producer 
with  the  outgoing  gases.  It  may  be  economized  chemically  by 
introducing  steam  into  the  producer,  which  absorbs  heat  by  its 
reaction  with  carbon — 

H20+C=CO+2H. 

The  decomposition  of  steam  is  attended  by  an  absorption  of 
29,100  units  of  heat,  while  but  2,416  units  are  evolved  in  the 
formation  of  carbon  monoxide.  It  is  seen  that  while  more  heat 


THE:  PREPARED  FUELS  43 

is  absorbed  than  is  evolved  in  the  above  reaction,  the  producer 
gas  is  enriched  with  carbon  monoxide  and  hydrogen,  and  a  quan- 
tity of  heat  equal  to  that  absorbed  is  regained  in  the  combustion 
of  the  hydrogen.1  This  does  not  take  into  account  the  heat  re- 
quired for  generating  the  steam,  which  is  done  outside  the  pro- 
ducer. The  greatest  economy  is  gained  when  just  enough  steam 
is  used  to  utilize  the  excessive  heat  in  the  producer.  The  amount 
of  steam  should  be  gaged  according  to  the  character  of  the  fuel 
used  and  other  conditions  in  the  producer,  and  it  is  best  deter- 
mined by  actual  experiment.  The  example  below  shows  the  loss 
of  calorific  power,  under  given  conditions,  when  a  solid  fuel  is 
converted  into  gas. 

The  materials  contributing  to  the  production  of  the  gas  are  — 

Carbon  (free)  ...................     30.78  per  cent. 

"       (combined)  .............     20.15  "       " 

Hydrogen  ......................       6.72"       " 

Oxygen  ........................     30.56  "       " 

Water  (steam)  ..................     "-79"       " 

Supposing  that  these  substances  are  converted  into  methane, 
carbon  monoxide  and  hydrogen  gases,  and  the  gases  cooled,  what 
is  the  loss  in  calorific  power? 

(1)  The  methane  is  the  sum  of  the  combined  carbon  and  the 
hydrogen,  or  26.87  Per  cent.,  by  weight,  of  the  combustible  gases. 

(2)  The  hydrogen  is  deduced  from  the  percentage  of  water  in 
the  mixture  — 

H2O:H2  ::  11.79  :X,  or  18:2  ::  ii.79:X   (  =  )    1.31  per  cent. 

(3)  The  carbon  monoxide  is  derived  from  the  free  carbon  — 
C:CO  ::  30.78  :X,  or   12:28  ::  30.78  :X   (  =  )   71.82  per  cent. 
The  combustible  elements  in  the  fuel  are  carbon  and  hydro- 

gen, and  their  ratios  are  — 

C  =          20.15  +  30.78  =  g 

6.72  +  20.15    +    30.78 


H= 


6.72  -f-  20.15  -f    30.78 
The  heating  power  of  the  fuel  before  the  conversion  is  — 
0.8834(8080)  +  o.i  166(34500)  =  1  1  161  calories. 

1  Hydrogen  burnt  to  steam  evolves  29,100  heat  units.     If  the  steam  is 
liquefied,  34,500  heat  units  are  evolved  . 


44  METALLURGY 

The  heating  power  of  the  gas  is — 
O.2687(i325o)+o.oi3i(345oo)-fo.7i82(5664)=8o8o  calories; 

The  loss  of  heating  power  is,  therefore,  11161 — 8080=3081 
calories,  or  the  efficiency  of  the  conversion  is  72  per  cent. 

With  the  precautions  to  prevent  loss  of  sensible  heat  in  the 
gases  and  careful  operation  of  the  producer,  the  efficiency  may 
be  as  high  as  90  per  cent.,  or  even  higher.  In  practice,  with  the 
best  modern  producers,  the  efficiency  is  commonly  placed  at  88 
per  cent.  The  following  example  is  taken  from  actual  practice 
in  which  the  Morgan  producer  was  used.1 

The  analyses  and  calorific  powers  of  the  coal  and  the  gas  are 
as  follows: 

COAI,  (CALCULATION  FOR  ONE  POUND). 

Ingredient  Percentage     Calorific  Power  in  British  Thermal  Units 

Carbon 50.87  o.  5087  X  14500    ==  7376 

Hydrocarbons 37-32  0.3732  X  2oooo2  =  7464 

14840 
GAS  (CALCULATION  FOR  i  cu.  FT.) 

Ingredient  Volume        Calorific  Power  in  British 

Thermal  Units 

Carbon  monoxide 0.245  78.37 

Hydrogen 0.178  57-66 

Methane 0.036  36.19 

Other  hydrocarbons 0.032  5°'93 

223.15 

I  lb.  of  coal  yields  55  Ibs.  of  gas,  which  when  cold  has  a 
calorific  power  of — 

55X223=12265  B.  T.  U. 
The  efficiency  is,  therefore — 

i oo (12265-^14840)  =89+  per  cent. 

Water  Gas. — Many  attempts  have  been  made  to  prepare  hydro- 
gen on  the  large  scale  from  water.  It  has  been  shown  that  more 
energy  is  expended  in  the  decomposition  of  water  than  is  de- 
veloped in  the  combustion  of  hydrogen.  Practically  pure  hydro- 
gen may  be  prepared  by  the  electrolysis  of  water  and  by  the 
reducing  action  of  some  metals  at  red  heat.  Since  carbonic  oxide 
is  itself  a  gas,  pure  hydrogen  does  not  result  from  the  decom- 

1  Calculations  taken  from  the  Morgan  Construction  Co's  catalog. 

2  This  value  is  estimated,  exact  information  not  being  at  hand  for  its 
determination. 


THE:  PREPARED  FUELS  45 

position  of  water  by  carbon,  but  the  result  is  a  mixture  of  the 
two  gases — 

H2O+C=:H2+CO. 

The  mixture  contains  theoretically  equal  volumes  of  hydrogen 
and  carbon  monoxide,  and  is  known  as  "water  gas."  The  com- 
mercial product  is  somewhat  variable  in  composition,  and  con- 
tains other  gases  as  impurities. 

Water  gas  is  manufactured  in  a  producer  of  similar  construc- 
tion to  the  ordinary  gas  producer.  Under  regular  working  con- 
ditions the  producer  carries  a  deep  bed  of  burning  coke.  Air  is 
blown  through  the  fuel  bed  from  the  bottom  until  it  is  heated  to 
incandescence.  The  resulting  gas,  which  is  of  poor  quality,  is 
carried  off  through  a  flue  at  the  top  of  the  producer.  The  blast 
is  now  shut  off  for  a  few  minutes  while  steam  is  introduced 
above  the  fuel  bed  and  drawn  downward  through  the  incandes- 
cent mass.  The  water  gas  resulting  from  its  decomposition  is 
taken  out  through  the  same  openings  by  which  the  air  blast  is 
introduced,  the  openings  into  the  air  and  gas  pipes  being  con- 
trolled by  means  of  valves. 

Water  gas  is  not  suitable  for  domestic  uses,  being  highly  pois- 
onous and  practically  odorless.  It  burns  with  a  pale-blue  flame, 
and  its  calorific  power  is  very  high.  It  has  been  employed  to 
some  extent  for  heating  high  temperature  furnaces. 

Typical  Analyses  of  Fuels. 
SOLIDS. 

Volatile 
Combustible 
Carbon  Hydrogen  Oxygen          matter          Fixed  Carbon         Ash 

Wood 50  6  42         (Nitrogen  2 )          ....  .... 

Peat 59  6  34 


Cannel  Coal 

Caking  Coal 

Coking  Coal 

Anthracite 

Charcoal 

Coke  (48  hours) 

Coke  (72  hours) 


46  34-5  19-5 

34  60.5  4.5 

25  68.  7. 

2   '  91.  7. 

§2. 

.10  10.02 

.62  10.56 


GASES. 

Methane         Other    Hydrogen      Carbon  Carbon  Nitrogen  Oxygen  Water 

Hydrocarbons  Monoxide  Dioxide 

Natural.-     93.5             0.5             I                0.5         0.25  4          0.25 

Coal  .....     42               3.5          45               6           0.5  i  i              i 

Water...        2                               45              45            4-5  1-5       *  I 

Producer        2.5            0.5             1.2          27            2  56 


CHAPTER  VI 


ORE  DRESSING. 

Ores. — Any  natural  substance  containing  metal  in  sufficient 
quantity  to  justify  its  extraction  is  an  ore.  The  amount  of  metal 
which  any  mineral  must  contain  to  be  an  ore  depends  upon  the 
price  of  the  metal  and  the  cost  of  preparing  it.  For  example, 
iron  ores  to  be  profitably  worked,  must  yield  nearly  half  of  their 
weight  in  metal,  while  gold  ores  may  be  treated  with  profit  if 
they  contain  but  a  fraction  of  an  ounce  of  gold  to  the  ton. 

The  metals  usually  occur  in  combination  with  non-metallic  ele- 
ments, though  some  occur  uncombined,  or  native.  The  ores  are 
usually  associated  with  some  non-metallic  material  such  as  earthy 
matter  or  rock.  This  is  known  as  vein-stuff,  or  gangue.  The 
summary  here  given  represents  practically  all  the  common  ores, 
showing  the  elements  with  which  the  several  metals  are  com- 
bined. The  groups  are  given  in  the  order  of  their  importance. 

Oxides Iron,  manganese,  chromium,  tin,  aluminum,  copper. 

Sulphides Copper,  lead,  zinc,  silver,  mercury,  iron. 

Carbonates Lead,  zinc,  iron,  copper. 

Native Copper,  silver,  gold,  platinum,  mercury. 

Silicates Zinc,  nickel . 

Arsenides Nickel,  cobalt. 

Chlorides Silver,  lead. 

Ore  Deposits. — The  various  formations  or  deposits  of  ores  be- 
long to  different  geological  ages.  It  is  not  definitely  known  how 
any  of  them  were  formed,  or  what  changes  they  have  undergone 
from  their  original  state.  There  is  much  conclusive  evidence  as 
to  both  physical  and  chemical  changes  affecting  ores,  gained 
from  a  study  of  the  earth's  crust,  and  from  the  changes  that  are 
now  in  progress.  The  position,  for  example,  of  some  ore  de- 
posits has  been  altered  by  upheavals  or  sinking  of  the  strata,  due 
to  earthquakes  and  other  disturbances,  while  immense  quantities 
of  ore  are  shown  to  have  been  transferred  from  place  to  place 
by  the  action  of  water.  The  deposits  of  ores  naturally  fall  into 
three  classes : — 


ORE    DRESSING  47 

Beds,  or  deposits  which  conform  to  the  direction  of  the  rock 
strata.  If  the  rocks  lie  in  horizontal  plains,  the  ore  beds  will  be 
flat ;  or  if  the  rock  strata  be  tilted,  the  ore  will  fill  the  space  be- 
tween. Many  deposits  of  this  class  have  been  formed  by  the 
action  of  water,  as,  for  example,  those  in  the  valleys  of  streams, 
known  as  alluvial  deposits.  The  most  famous  ore  beds  are  those 
of  Lake  Superior,  bearing  iron. 

Veins  or  Lodes. — A  great  many  ores  are  found  in  what  appear 
to  be  fissures  or  cracks  in  the  earth's  crust.  They  do  not  con- 
form to  the  stratification  of  the  rocks,  but  cut  through  the  rock- 
mass  at  any  angle.  Such  deposits  are  known  as  veins.  They 
may  vary  in  thickness  and  in  the  direction  of  their  extent.  The 
continuity  is  often  broken  off  suddenly,  due  to  faulting  in  the 
earth's  crust. 

Pocket  ores  are  those  which  are  found  in  small  patches  or 
cavities.  They  are  often  met  with  in  the  vicinity  of  veins.  Pocket 
ores  are  often  of  excellent  quality,  but  so  scattered  as  to  be  un- 
profitable for  mining. 

The  extraction  of  a  metal  and  its  preparation  for  the  market 
involves  a  number  of  processes.  The  details  of  a  process  depend 
upon  the  physical  and  chemical  properties  of  both  the  ore  and 
the  metal.  There  are  usually  four  distinct  operations,  or  classes 
of  operations,  from  the  first  treatment  of  the  ore  to  the  last  work 
on  the  finished  metal. 

1.  Preliminary  Treatment  of  the  Ore  or  Ore  Dressing. — The  ob- 
ject of  this  step  is  to  concentrate  the  ore  as  much  as  possible, 
and  to  render  it  more  suitable  for  the  next  operation. 

2.  Extraction  of  the  Metal. — This  consists  in  the  practical  iso- 
lation of  the  metal  from  the  elements  with  which  it  was  com- 
bined, and  in  disengaging  it  from  the  gangue.     A  process   in 
which   this  is  accomplished  by   fusion  of  the  metal   is  termed 
smelting.    Other  processes  depend  upon  the  solution  of  the  metal 
in  mercury  and  subsequent   separation — amalgamating,   while  a 
third  class  of  processes  employs  an  aqueous  solvent  from  which 
the  metal  is  precipitated — wet  processes. 

3.  Refining. — It  is  not  practicable  in  most  instances  to  recover 
metals  in  a  sufficiently  pure  state  by  a  single  operation.  The  pro- 


48  METALLURGY 

cess  of  refining  involves  one  or  more  operations  by  which  the 
foreign  elements  are  removed  or  the  amount  to  be  left  is  fixed. 

4.  Mechanical  Treatment. — This  includes  hammering,  rolling, 
reheating,  casting  and  all  purely  mechanical  operations  which 
have  for  their  aim  the  development  and  improvement  of  the 
properties  of  metals,  or  the  manufacture  of  them  into  finished 
products. 

The  first  and  fourth  classes  of  operations,  as  defined  above,  do 
not  belong  strictly  to  the  field  of  metallurgy,  the  first  belonging 
more  to  that  of  mining  and  the  last  to  mechanics.  As  an  industry, 
metallurgy  is  closely  associated  with  mining  and  mechanical  en- 
gineering, and  these  operations  may  be  looked  upon  as  connect- 
ing links  of  the  three  industries. 

A  great  deal  may  be  gained  by  dressing  ores.  In  the  first 
place,  the  ore  may  be  greatly  concentrated,  reducing  the  cost  of 
transportation,  lessening  the  amount  of  fuel  needed  for  smelting 
and  increasing  the  output ;  secondly,  it  may  be  possible  to  remove 
or  greatly  diminish  the  quantity  of  those  ingredients  of  the  ore 
which  would  contaminate  the  metal ;  lastly,  the  ore  is  delivered  to 
the  smelter  in  more  convenient  shape  and  of  more  uniform  com- 
position. Under  such  conditions  the  process  of  smelting  may  be 
conducted  with  greater  regularity  and  efficiency  than  would 
otherwise  be  possible. 

Of  the  processes  used  in  dressing  ores  the  more  common  are 
weathering,-  hand-picking,  breaking,  pulverizing,  screening, 
washing,  magnetic  separating,  calcining  and  roasting. 

Weathering. — Some  ores  are  much  improved  after  long  ex- 
posure to  the  weather.  During  the  freezes  of  winter  the  lumps 
are  split  up,  the  ore  cleaving  and  falling  away  from  the  rocks 
with  which  it  is  associated.  Impurities  may  be  rendered  soluble 
by  the  action  of  the  atmosphere  and  leached  out  by  the  rains,  or 
the  metallic  portion  itself  may  be  recovered  directly  in  this  way. 
Weathering  processes  are  necessarily  slow,  often  requiring  years, 
and  yet  they  offer  the  only  feasible  means  of  treating  some  ores. 

Hand  Picking. — This  method  of  concentration  depends  entirely 
upon  the  intelligence  of  laborers  to  select  the  ore  from  the  worth- 
less material  in  which  it  is  imbedded.  Some  very  undesirable  im- 


ORE  DRESSING 


49 


_  _„ vu- , — i— - y&r--  -4-t 


.  Fig.  15— Blake  Crusher.     (Allis-Chaltners  Co.) 

AA,  still  bearings  for  toggle  plates  ;  B,  flywheel ;  D,  driving  pulley  ;  E,  Pitman 

G,  toggle  plates  ;  H,  fixed  jaw  ;  I,  checks ;  J,  movable  or  swing  jaw;  K,  bar  ; 

I,,  set  screws  for  toggle  block  ;    N,  wedge  adjusting  stud  ;  O,  toggle  block  ; 

PP,  jaw  plates  ;  R,  rubber  spring  ;  S,  rod  ;  W,  wedge  block. 


50  METALLURGY 

purities  may  be  seen  and  rejected  in  this  way.  Hand  picking  is 
not  employed  except  with  ores  of  a  high  market  value  or  in 
countries  where  labor  is  cheap. 

Breaking. — Ores  occurring  in  masses  of  rock  must  be  reduced 
to  small  lumps,  so  that  in  subsequent  treatment  they  will  be  ex- 
posed more  fully  to  the  action  of  heat  or  chemical  agencies. 
There  are  two  types  of  rock  and  ore  breakers  in  general  use,  viz., 
jaw  crushers,  of  which  the  Blake  machine  is  a  well  known  repre- 
sentative, and  gyratory  crushers,  of  which  the  Gates  machine 
is  a  good  example. 

The  mechanism  of  the  Blake  machine  is  well  illustrated  in  Fig. 
15.  The  ore  is  crushed  between  two  jaws,  one  of  which  is  sta- 
tionary. The  swinging  jaw  is  driven  by  a  powerful  toggle  move- 
ment communicated  from  the  revolving  shaft.  The  shaft  carries 
two  heavy  fly-wheels  and  the  driving  pulley.  The  crushing  jaws 
are  faced  with  hard  steel  plates.  The  machine  is  adjustable  for 
crushing  to  different  sizes:  the  jaws  being  brought  closer  together 
by  the  use  of  longer  toggle  plates. 

A  vertical  section  of  the  gyratory  crusher  is  shown  in  Fig.  16. 
In  this  machine  the  ore  is  crushed  by  the  action  of  a  gyrating 
spindle  within  a  circular  shell  of  steel.  The  outer  shell  of  the 
machine  is  made  in  two  sections  bolted  together,  the  lower  sec- 
tion being  supported  on  the  base  plate  and  the  upper  section 
carrying  the  hopper  for  receiving  the  ore  and  the  "  spider"  which 
furnishes  the  upper  tearing  for  the  spindle.  The  lower  part  of 
the  spindle  has  a  journal  bearing  in  the  eccentric  hub  of  a  bevel 
gear,  the  gear  having  a  bearing  concentric  with  its  own  rotation 
in  the  base  plate.  The  gear  meshes  with  a  bevel  pinion  which, 
with  the  driving  pulley,  is  carried  on  a  horizontal  shaft.  To 
the  head  of  the  spindle  is  keyed  a  bushing  by  which  the  spindle 
is  supported  and  adjusted  at  different  heights.  In  the  hub  of 
the  spider  is  secured  a  bushing  to  carry  the  weight  of  the  spindle, 
and  also  to  furnish  the  upper  bearing.  The  spider  bushing  has 
a  spherical  top,  and  the  spindle  bushing  has  a  socket-shaped 
flange  which  rests  upon  this.  The  cylindrical  bearing  is  tapered 
slightly  to  permit  of  the  gyratory  motion  of  the  spindle. 
The  crushing  head  of  the  spindle  has  the  shape  of  a 


Fig.  16— Gates  Rock  and  Ore  Breaker.     (Allis-Chalmers  Co.) 


Fig.  17— Stamp  Battery.     (Allis-Chalmers  Co.) 


ORE   DRESSING  51 

truncated  cone,  and  the  shell  around  it  resembles  an  inverted 
truncated  cone.  A  circular,  V-shaped  space  is,  therefore,  left 
between  the  crushing  surfaces.  The  crushing  surfaces  are  of 
chilled  iron  or  hardened  steel.  The  shell  is  lined  with  steel  die 
plates  which  are  renewable. 

When  the  machine  is  run  empty  the  spindle  is  free  to  rotate 
with  the  gear,  but  when  a  lump  of  stone  is  introduced  it  can  not 
rotate,  but  retains  the  gyratory  motion.  The  crushing  head  is 
brought  successively  near  the  opposite  surface  in  the  direction  of 
the  gyration,  and  as  one  side  of  the  head  approaches  the  shell 
the  opposite  side  recedes  from  it.  As  the  pieces  are  reduced  in 
size  they  settle  by  gravity  until  they  fall  between  the  bottom 
edges  of  the  crushing  surfaces.  The  material  is  carried  out  by 
a  chute  which  passes  through  the  side  of  the  lower  section  of 
the  shell. 

It  may  be  seen  from  the  illustration  that  by  raising  the  spindle 
the  ore  will  be  crushed  to  smaller  size.  The  spindle  is  raised  for 
this  purpose,  and  as  the  wear  increases  the  size  of  the  opening 
between  the  crushing  surfaces. 

Pulverizing. — Many  ores  must  be  reduced  to  powder  before 
the  metal  or  metallic  portion,  which  exists  in  such  minute  par- 
ticles, can  be  disentangled.  This  is  done  by  stamping  or  grind- 
ing after  the  preliminary  breaking.  Of  the  variety  of  mills  in 
use  for  pulverizing  ores  the  stamp  mill  is  the  most  adaptable.  The 
general  arrangement  of  a  gravity  stamp  mill  is  shown  in  Fig.  17. 
The  stamps  are  arranged  in  groups  of  five,  and  are  lifted  in  a  cer- 
tain order  by  cams  set  at  different  angles  on  the  driving  shaft. 
The  stamps  drop  by  gravity  upon  dies  placed  in  the  mortar.  The 
heads  of  the  stamps  are  armed  with  hard  steel  shoes,  and  the 
dies  are  of  the  same  material.  The  mortars  are  cast  iron.  The 
ore  is  fed  into  the  mortars  from  a  hopper  behind  the  battery,  and  as 
it  is  pulverized  under  the  stamps  it  is  distributed  by  them  and 
thrown  against  the  screens  which  are  set  in  front.  The  ore  that 
is  sufficiently  pulverized  passes  through  the  screens  and  is  taken 
away  for  further  treatment. 

The  stamping  process  is  made  more  rapid  by  the  use  of  water 
in  the  mortars.  The  water  mav  be  added  intermittentlv  or  con- 


52  METALLURGY 

tinuously.  If  a  large  quantity  of  water  is  not  objectionable  with 
the  pulp,  a  continuous  stream  is  allowed  to  run  into  the  mor- 
tars. This  in  passing  out  through  the  screens  carries  away  the 
fine  ore,  and  the  mortars  are  kept  cleaner  than  they  are  .when 
the  ore  is  crushed  dry. 

Fig.    1 8  shows  the  section  of  a  mortar  with  the  screen   in 


Fig.  18. 

position.  The  opening  at  the  back  is  for  the  intake  of  ore.  The 
mortar  is  lined  with  steel,  and  amalgamated  copper  plates  are 
bolted  in  the  front  and  back  when  gold  ores  are  treated.  Where 
laige  crushing  capacity  is  desired,  double  discharge  mortars  are 


Fig.  19— Chilian  Mill.     (Allis-Chalmers  Co.) 


Fig.  20— Huntingtcn  Mill.     (Allis-Chalmers  Co. 


ORE  DRESSING  53 

usecl.     These  are  designed  for  wet  crushing  and  are  equipped 
with  screens  both  in  front  and  behind. 

The  Chilian  Mill. — This  mill  consists  of  a  circular  iron  pan 
upon  which  two  or  three  heavy  rollers  revolve  (Fig.  19).  The 
rollers  turn  upon  a  horizontal  axle,  which  is  driven  by  a  vertical 
shaft.  The  tires  of  the  rollers  are  of  hard  steel,  as  is  also  the 
plate  upon  which  they  travel.  Being  placed  near  the  center  of 
the  pan,  the  rollers  are  twisted  at  the  same  time  they  are  re- 
volved upon  the  track,  with  the  result  that  the  ore  is  ground 
rapidly  and  very  fine.  The  ore  is  fed  upon  the  pan  by  an  auto- 
matic device,  and  it  is  thrown  constantly  in  the  path  of  the 
rollers  by  scrapers  which  are  carried  on  the  revolving  shaft.  The 
discharge  screen  is  placed  at  the  side,  the  ore  being  thrown 
against  it  by  the  action  of  the  rollers. 

The  Huntington  Mill. — This  mill  also  grinds  with  rollers,  but 
unlike  the  Chilian  mill,  there  is  no  twisting  of  the  rollers  upon 
the  surface  of  the  ring-die.  The  rollers,  of  which  there  are  four, 
are  suspended  from  a  plate  which  revolves  with  a  vertical  shaft 
passing  through  the  center  of  the  machine.  The  shaft  is  geared 
to  a  horizontal  pully  shaft.  The  rollers  are  free  to  revolve  on 
their  own  spindles,  and  when  the  mill  is  in  operation  they  swing 
by  centrifugal  force  against  the  side  of  the  pan  enclosing  them. 
The  ring-die  upon  which  they  revolve  is  of  hardened  steel.  One 
inch  of  space  is  allowed  between  the  rollers  and  the  bottom  of 
the  pan.  The  discharge  screens  are  placed  above  the  rollers, 
over  the  openings  shown  in  the  cut  (Fig.  20). 

The  Huntington  mill  is  designed  for  wet  grinding,  and  is  par- 
ticularly adaptable  to  the  grinding  and  amalgamating  of  soft 
gold  ores.  The  mercury  is  held  in  the  bottom  of  the  pan,  where 
it  is  not  disturbed  by  the  movement  of  the  rollers. 

Screening. — Ores  are  classified  by  passing  their  finer  particles 
through  screens,  the  holes  in  which  are  of  definite  size.  The 
holes  in  screens  differ  in  shape  from  round  to  square  and  oblong, 
each  shape  being  suited  to  the  character  of  material  to  be  treated. 
The  coarsest  screens,  such  as  are  used  for  sizing  coal,  commonly 
consist  of  parallel  bars,  determinately  spaced,  and  held  in  posi 
tion  by  means  of  bolts.  Such  a  device  is  called  a  "grizzly"  or 


54  METALLURGY 

bar  screen.     Grizzlies  are  generally  placed  at  an  incline  and  thej 
ore  is  thrown  upon  the  upper  ends  of  the  bars  and  moved  by  I 
gravity  in  the  direction  of  their  length.    The  smaller  screens  are  j 
of  perforated  plate  or  sheet  metal  or  of  wire  cloth.     The  finest  I 
screens  are  necessarily  made  of  cloth.    The  size  of  the  mesh,  i.  e.,  I 
the  spaces  between  the  wires,  determines  the  size  of  the  grains  I 
that  pass   through.     The   sizes   are   known   by   the   number   of 
meshes  per  linear  inch.    In  the  operation  of  screening  the  screen 
is  either  placed  in  an  inclined  position,  so  that  the  ore  may  be  fed 
upon  it  and  moved  by  gravity,  or  the  screen  is  operated  mechan- 
ically to  move  the  ore.     Some  screens  are  made  in  the  shape  of 


Fig.  21. 

cylinders,   which  are  revolved,   and   others   are   plane   surfaces, 
which  are  shaken  by  suitable  means. 

Washing. — This  subject  comprises  a  large  number  of  processes 
conducted  in  entirely  different  ways.  All  methods  of  ore  wash- 
ing make  use  of  the  same  principles,  though  the  character  of 
certain  ores  requires  special  methods.  Reference  is  here  made 
to  hydraulicing,  and  to  washing  by  means  of  riffles  and  sluices, 
described  in  Chapter  XXVI.  The  jig,  which  is  of  more 
general  application  in  the  washing  of  coarse  ore,  and  the 
frue  vanner,  most  commonly  used  for  washing  pulverized  ore,  are 
described  below.  Fig.  21  gives  the  vertical  section  through  two 


ORE   DRESSING  5^ 

compartments  of  a  jig.  The  jig  consists  essentially  of  a  sieve 
or  a  set  of  sieves  upon  which  the  ore  is  held,  while  water  is 
forced  upward  through  the  ore  by  means  of  a  piston,  or  the  sieve 
itself  is  moved  in  the  water.  Jigs  with  stationary  sieves  are  the 
more  common.  As  shown  in  the  illustration,  the  sieves  are  placed 
over  the  water  compartments,  to  which  hydraulic  water  is  sup- 
plied through  pipes  at  AA.  The  downward  movement  of  the 
piston  forces  the  water  in  both  compartments  upward  through 
the  sieves,  upon  which  the  ore  is  placed.  The  water  overflows 
at  the  top,  carrying  with  it  the  light,  earthy  matter  and  leaving 
the  larger  and  heavier  particles  of  ore  upon  the  sieve.  Some 
jigs  are  built  with  a  number  of  compartments,  the  ore  being  dis- 
charged from  one  sieve  to  the  next,  which  is  placed  on  a  lower 
level.  Jigs  are  commonly  built  of  wood,  the  parts  which  are  sub- 
ject to  greatest  wear  being  of  iron. 

The  frue  vanner  is  shown  pictorially  in  Fig.  22.  The  im- 
portant parts  of  this  machine  are  the  broad,  rubber  belt  traveling 
over  the  end  rollers ;  the  shaking  table  underneath  the  upper  span 
of  the  belt;  the  ore  spreader,  and  the  water  distributor.  The 
main  shaft,  carrying  the  driving  pulley,  is  located  on  the  side  of 
the  machine  and  turns  the  forward  belt  roller  by  means  of  the 
worm  gear  as  shown  in  the  cut.  The  whole  mechanism  is  held 
on  a  stout  wooden  frame  bolted  together  and  carried  on  iron 
supports. 

The  belt  is  flanged  at  the  edges  to  prevent  material  from  pass- 
ing over.  The  upper  span  of  the  belt,  which  forms  the  concen- 
trating table,  is  supported  between  the  end  rollers  on  small  rollers 
carried  by  the  shaking  table.  The  end  rollers  are  adjustable  at 
different  levels,  so  that  when  the  machine  is  in  operation  the  belt 
forms  a  moving,  inclined  plane,  the  direction  of  the  motion  being 
up-hill.  In  addition  to  this  motion  the  belt  is  shaken  gently  by 
lateral  jerks.  This  is  done  by  the  shaking  table,  which  in  turn 
receives  its  motion  from  a  crank-shaft  attached  to  the  driving- 
shaft  of  the  machine. 

In  operating  the  frue  vanner  the  ore  mixed  with  water  is  sup- 
plied to  the  feeder,  which  spreads  it  in  a  thin  stream  upon  the 
belt.  The  water  flows  down  the  incline,  carrying  the  lighter 


56  METALLURGY 

particles  of  solid  matter  with  it.  But  the  bulk  of  the  ore  is  car- 
ried forward  on  the  belt  until  it  passes  under  the  water  distrib- 
utor. This  is  placed  at  a  short  distance  up  the  incline  from  the 
ore  spreader.  It  is  supplied  with  clear  water,  which  it  distributes 
from  small  nozzles,  spaced  a  few  inches  apart  and  in  line  across 
the  belt.  The  water  acts  upon  the  layer  of  material  according  to 
the  character  of  the  particles  it  contains.  Heavy  particles  or 
grains  will  be  left  undisturbed  or  moved  but  a  short  distance, 
while  the  light  particles  are  washed  down  the  incline.1  The  , 
concentrate,  which  is  the  metal-bearing  portion  of  the  ore,  is 
carried  by  the  belt  to  the  upper  end  of  the  incline,  where  it  falls 
into  a  tank  placed  to  receive  it,  and  the  earthy  matter  is  borne 
with  the"  sheet  of  water  to  waste  at  the  lower  end.  The  belt  is 
washed  by  causing  the  lower  span  to  dip  under  water. 

The  lateral  shaking  of  the  belt  keeps  the  grains  in  motion  and 
prevents  the  water  from  forming  channels  and  separating  to  a 
considerable  extent  from  the  solid  matter.  The  incline  of  the 
belt  and  the  rapidity  of  the  movement  require  adjustment  for  dif- 
ferent kinds  of  ore.  The  supply  of  water  with  the  ore  and  the 
clear  water  are  also  regulated  to  suit  different  conditions. 

Magnetic  Separating. — This  process  was  first  suggested  by 
Abraham,  of  Sheffield,  in  1882. -  It  is  applicable  to  any  ore  con- 
taining a  magnetic  ingredient,  whether  that  ingredient  is  to  be 
saved  or  rejected.  The  ore  must  be  dry  and  so  finely  divided 
that  the  magnetic  and  non-magnetic  portions  do  not  adhere. 
Magnetic  separators  are  of  different  types,  each  type  being 
adapted  to  special  work.  The  older  machines  are  adaptable  only 
tc  highly  magnetic  material.  These  machines  employ  separating 
rollers  or  drums,  which  are  magnetized  electrically.  The  rollers 
are  revolved  in  the  horizontal  position,  while  a  thin  stream  of 
the  pulverized  ore  is  fed  upon  them  from  a  hopper  above.  The 
non-magnetic  particles  in  the  ore  fall  immediately  from  the  rollers 

1  The  principle  here  involved  may  be  easily  illustrated  by  pouring  sus- 
pended mineral  matter  of  varying  specific  gravity  upon  a  suitable,  inclined 
plane  and  applying  a  jet  of  water.  The  lighter  particles  are  carried  away, 
and  the  heavier  ones  are  left  at  different  distances  from  the  starting  point. 

3  Dingler's  Poly.  Jour.,  288,  203-209. 


Fig.  23 — Principle  of  the  Wetherill,  Type   "  E"  Separator. 


ORE:  DRESSING  57 

and  the  magnetic  portion  is  detached  by  brushes  which  bear  upon 
the  rollers  farther  around. 

The  Wetherill  separator  is  designed  for  concentrating  weakly 
magnetic  minerals.  These  machines  operate  upon  the  principle 
shown  in  Fig.  23.  The  ore  is  distributed  over  the  con- 
veyor belt,  B,  by  means  of  the  feed  roller  under  the  hop- 
per. The  conveyor  belt  passes  between  two  horse-shoe  elec- 
tro-magnets, which  are  supported  in  the  position  shown.  The 
poles  of  the  upper  magnet  are  wedge-shaped,  while  those  of  the 
lower  magnet  are  flattened.  The  paramagnetic  minerals  are  more 
strongly  attracted  by  the  upper,  wedge-shaped  poles  than  by  the 
lower  ones,  so  that  the  tendency  of  the  magnetic  particles  is  to 
cling  to  the  upper  poles  as  they  are  brought  into  the  magnetic 
field.  The  magnetic  particles  jump  upward,  but  they  do  not 
come  in  actual  contact  with  the  poles,  since  the  thin  cross-belts, 
B1,  pass  closely  under  the  upper  poles.  The  ore  adheres  to  these 
until  it  is  carried  by  them -out  of  the  magnetic  field.  The  non- 
magnetic particles  of  ore  fall  from  the  conveyor  belt  as  it  passes 
over  the  forward  pulley.  Fig.  24  is  a  pictorial  view  of  the  Weth- 
erill separator. 

Calcining  and  Roasting. — These  two  terms  are  used  somewhat 
interchangeably  among  metallurgists.  A  distinction,  however, 
should  be  made.  To  calcine  a  subtance  is  to  drive  off  volatile 
matter  by  heating.  It  differs  from  distillation,  since  the  volatile 
matter  is  not  recovered.  To  roast  a  subtance  is  to  heat  it  while 
adding  something  to  react  chemically  with  it. 

Examples  of  calcining  are  afforded  by  the  heating  of  oxidized 
ores  to  drive  off  the  water,  and  in  the  "  burning  "  of  limestone, 
dolomite,  etc.,  to  expel  carbon  dioxide.  The  process  is  generally 
conducted  in  kilns  (p.  60). 

Ores  are  commonly  roasted  to  convert  sulphides  into  sulphates 
and  oxides — oxidizing  roasting,  or  into  chlorides — chloridizing 
roasting.  In  the  first  instance  the  air  plays  the  important  part 
in  the  elimination  of  sulphur,  while  in  the  latter  chlorine  must  be 
supplied. 

Mixing  Ores. — Aside  from  the  foregoing  methods  of  concentrat- 
ing ores  and  eliminating  impurities  from  them,  may  be  mentioned 


58  METALLURGY 


the  mixing  of  ores  of  different  grades.  It  is  highly  desira 
that  the  raw  materials  for  any  process  be  uniform  in  composi- 
tion, and  especially  is  this  true  in  the  case  of  ores.  Suppose,  for 
example,  that  three  iron  ores  are  delivered  to  the  smelter,  con- 
taining 3,  6  and  9  per  cent,  of  silica  respectively.  By  mixing 
equal  parts  of  numbers  one  and  three  with  number  two,  a  mix- 
ture is  obtained  which  averages  6  per  cent,  in  silica.  Some  poor 
ores  may  be  profitably  smelted  by  mixing  them  with  richer  ores, 
when  there  is  no  other  feasible  way  of  utilizing  them. 


CHAPTER  VII 


FURNACES. 

Most  of  the  improvements  which  have  marked  the  development 
of  modern  practice  in  metallurgy  have  been  mechanical.  Fur- 
naces have  been  altered  in  form  and  increased  in  capacity,  and 
machinery  has  been  introduced  and  improved  to  meet  the  increas- 
ing demands  for  larger  yields  of  metal.  Metallurgical  processes 
are  primarily  chemical,  the  first  problems  which  they  present  in- 
volving principles  in  chemistry.  Application  is  made  of  these 
principles  in  the  intelligent  selection  of  materials  for  constructing 
furnaces,  in  the  use  of  fuel,  and  in  the  isolation  of  metals  from 
their  compounds.  Improvements  in  metallurgical  processes,  as 
above  indicated,  have  been  largely  the  work  of  engineers. 

The  first  and  most  intricate  problem  in  the  designing  of  fur- 
naces is  to  determine  what  should  be  the  form  and  size.  These 
features  are  affected  by  the  character  of  the  fuel  and  material 
treated,  the  method  of  heating  and  temperature  required,  and  the 
nature  of  the  process  in  general.  The  next  consideration  is  the 
materials  out  of  which  the  furnace  should  be  built.  The  cheapest 
materials  that  will  answer  are  not  always  the  cheapest  in  the  end, 
but  those  that  will  endure  the  longest  campaigns  are  generally 
the  most  economical. 

For  that  all  important  part  of  the  furnace,  the  lining,  a  material 
of  reasonable  cost  is  selected  that  will  best  withstand  the  conditions 
inside  the  furnace.  As  a  means  of  preserving  the  linings  of  fur- 
naces water  cooling  is  often  resorted  to,  especially  if  the  lining  is 
exposed  to  the  scorifying  action  of  molten  materials.  One  method 
of  cooling  is  to  introduce  hollow  blocks  of  metal  into  the  furnace 
wall,  maintaining  a  circulation  of  cold  water  through  the  blocks. 
Another  method  is  to  line  the  wall  on  the  outside  with  a  water 
jacket,  i.  e.,  a  shell  of  metal  through  which  water  is  circulated, 
in  some  instances  the  refractory  lining  is  dispensed  with  alto- 
gether and  the  water  jacket  substituted. 


60  METALLURGY 

On  account  of  the  high  cost  of  most  refractory  materials  the 
outer  walls  and  foundations  of  furnaces  are  commonly  built  of 
common  brick  or  stone.  In  most  furnaces  the  masonry  is  reen- 
forced  with  iron.  One  method  of  supporting  the  brick  work  is  to 
construct  a  frame  of  iron  or  steel  beams  and  tie-rods.  The  beams 
are  set  vertically  or  horizontally  against  opposite  walls  and  secured 
with  the  tie-rods.  Metal  bands  may  be  used  for  supporting  round 
structures.  It  is  often  necessary  to  provide  a  means  of  tighten- 
ing and  loosening  the  framework  on  account  of  the  contraction 
and  expansion  of  the  walls.  Furnace  walls  are  most  completely 
reenforced  by  encasing  them  in  iron  plates  rivetted  together  to 
form  a  shell.  Cast  iron  or  structural  columns  are  often  used  in 
the  foundation  work  to  carry  the  superstructure  of  a  furnace  in- 
stead of  the  more  cumbersome  masonry. 

The  principal  types  of  furnaces  are  classified  and  defined  here 
with  the  object  of  simplifying  their  descriptions  later.  Furnaces 
may  be  divided  into  four  general  classes,  many  variations  being 
found  in  each  class. 

i.  Furnaces  in  which  the  Fuel  and  the  Substance  are  Treated  in 
Contact. — Under  this  class  belong  kilns,  blast  furnaces  and 
forges  or  shallow  hearths. 

Kilns. — This  type  of  furnace  is  employed  exclusively  for  cal- 
cining and  roasting.  As  an  example  of  the  stationary  kiln  the 
Cleveland  or  Gjer's  kiln  may  be  taken  (Fig.  25).  This  is  cylin- 
drical in  form,  the  walls  sloping  inward  toward  the  bottom.  The 
walls  are  constructed  of  boiler  plates  and  lined  with  fire-brick.  The 
superstructure  is  supported  on  short  columns  of  cast  iron.  Up- 
on the  floor  of  the  kiln  are  laid  cast  iron  plates.  In  the  illustra- 
tion the  lower  part  of  the  wall  is  cut  away  to  show  the  interior, 
and  especially  the  cast  iron  cone  which  is  fixed  centrally  upon  the 
floor  of  the  kiln.  This  cone  serves  to  throw  the  charge  outward, 
so  that  it  will  descend  continuously  as  the  floor  is  cleared.  The 
fuel  is  charged  with  the  material  to  be  calcined  at  the  top.  The 
small  doors  near  the  bottom  are  for  the  admittance  of  air. 

The  rotary  kiln  is  cylindrical  in  form,  and  it  is  revolved  me- 
chanically in  the  horizontal  or  slightly  inclined  position.  It  is 
fired  with  soft  coal,  which  is  pulverized  and  blown  in  with  a 


FURNACES 


61 


forced  draft.     This  style  of  furnace,  now  universally  employed  in 
calcining  cement  has  but  limited  application  in  metallurgy. 

Blast  Furnaces. — By  these  are  meant  the  tall  structures,  or  those 
whose  height  is  greater  than  their  diameter  using  a  blast  of  air. 


n 


-  25. 


Among  these  may  be  included  the  furnaces  now  generally  used  for 
smelting  iron,  copper,  and  lead  ;  cupolas  for  remelting  metals,  and 
converters  for  refining.  Descriptions  and  illustrations  of  blast 
furnaces  will  be  found  on  pages  78,  87,  189  and  217. 

Forges.  —  At  one  time  this  term  was  used  to  denote  the  peculiar 
form  of  hearth  used  in  iron  smelting.  It  has  a  more  general  mean- 


62  METALLURGY 

ing  now,  though  it  usually  refers  to  the  smith's  forge,  or  any 
kind  of  wind  furnace  for  reheating  metal,  without  fusion,  and 
in  contact  with  fuel. 

2.  Furnaces  in  which  the  Substance  Treated  is  in  Contact  with 
the  Flame  and  Products  of  Combustion,  but  not  in  Contact  with 
Solid  Fuel. — Under   this    class    belong   the    many    types    of    re- 
verberatory  furnaces.  Reverberatories  are  the  most  common  of 
all  furnaces,  serving  a  great  variety  of  purposes.     The  distinct- 
ive features  in  their  construction  are  the  separate  hearth  or  fire- 
place in  which  the  fuel  is  burnt,  or  an  arrangement  for  gas;  the 
low  arched  or  dome-shaped  roof  which  deflects  the  flame  and  heat 
on  to  the  hearth,  and  the  stack  for  maintaining  the  draft.     Rever- 
beratory  furnaces  are  usually  fired  with  soft  coal  or  gas.     A  typi- 
cal form  is  illustrated  on  p.  127. 

Mechanical  Reverberatories  have  been  introduced  and  in  many 
processes  they  have  been  generally  adopted.  Among  these  are 
mentioned  roasting  furnaces  with  automatic  stirrers  (p.  178),  and 
the  rocking  and  tilting  furnaces  used  in  steel  manufacture  (p. 

156). 

3.  Furnaces  in  which  the  Substance  Treated  is  not  in  Contact 
with  either  the  Fuel  or  the  Products  of  Combustion. — Furnaces 
of  this  class  bear  no  relation  to  each  other,  except,  in  that  all  are 
designed  to  shield  the  ore  or  metal  from  the  action  of  fuel  or  gases 
while  heat  is  being  applied.     The  furnaces  so  constructed  are  fitted 
with  muffles,  crucibles  or  retorts,  as  the  case  may  require. 

Muffle  Furnaces  are  principally  used  for  roasting  ores  which 
require  a  strongly  oxidizing  atmosphere,  or  in  general,  when  the 
temperature  and  atmosphere  about  the  substance  are  to  be  careful- 
ly controlled. 

Crucible  Furnaces  are  used  in  refining,  alloying  and  remelt- 
ing  operations  in  general,  in  which  small  amounts  of  metals  are 
treated.  The  crucibles  are  heated  by  means  of  a  flame  and  hot 
gases,  or  by  direct  contact  with  glowing  coals.  A  closely  fitting 
lid  protects  the  contents  of  the  crucible  entirely  from  the  fuel  and 
gases.  A  description  of  the  manufacture  of  crucibles  and  of  a 
crucible  furnace  is  given  under  the  subject  of  Crucible  Steel. 

Retort  Furnaces  are  employed  for  the  distillation  of  volatile 
metals  from  their  ores  or  from  alloys.  They  are  used  in  the 


FURNACES  63 

smelting  of  zinc  and  mercury,  and  in  some  refining  processes 
where  these  metals  are  to  be  separated  from  others.  The  by- 
product coke  ovens  afford  other  examples  of  retort  furnaces. 

4.  Electric  Furnaces. — According  to  Moissan,  as  early  as  1849, 
Despretz  made  use  of  the  heat  of  an  electric  arc,  the  current  hav- 
ing been  derived  from  a  battery.  Whatever  may  have  been  sug- 
gested to  later  workers,  the  electric  furnace  was  not  developed 
until  the  cost  of  the  current  was  lessened  by  the  dynamo.  Siemens, 
Moissan  and  Huntington  were  pioneers  in  the  construction  of  elec- 
tric furnaces.  The  more  recent  furnaces,  designed  for  large  op- 
erations have  been  built  by  Cowles,  Hall,  Acheson  and  others. 

Electric  furnaces  are  generally  of  simple  construction.  All  of 
them  make  use  of  the  heat  evolved  by  the  resistance  offered  to  the 
passage  of  an  electric  current.  The  resistance  may  be  due  to  a 
conductor  of  low  conductivity  or  to  an  arc  or  to  both.  In  many 
instances  the  material  that  is  being  treated  in  the  furnace  is  placed 
in  the  circuit  to  act  as  a  resistance. 

Regenerative  Firing. — The  heat  generator  was  introduced  in 
1817  by  Robert  Stirling  (Whitwell).  The  regenerative  system 
as  now  used,  is  due  chiefly  to  William  and  Frederick  Siemens. 
The  regenerator  is  a  storage  chamber  for  surplus  heat;  an  ap- 
paratus for  retaining  a  portion  of  the  waste  heat,  and  returning  it 
to  the  furnace  from  which  it  was  taken.  The  products  of  com- 
bustion, and  in  some  cases,  the  combustible  gases  themselves,  which 
•can  not  be  utilized  in  the  furnace,  are  led  into  the  regenerator 
where  a  large  part  of  their  sensible  heat  or  the  heat  of  their  com- 
bustion is  absorbed.  A  part  of  this  heat  is  returned  to  the 
furnace  by  passing  the  air  or  gas  supplied  to  the  furnace  through 
the  regenerator. 

Retrospective. — The  foregoing  chapters  have  dealt  with  the 
•general  principles  underlying  the  science  of  metallurgy ;  materials 
used  in  the  art  or  industry  of  metallurgy,  and  processes  affecting 
the  industry  at  large.  The  subsequent  chapters  will  deal  largely 
with  these  principles  as  applied  to  practical  ends.  It  is  the  aim  in 
this  text  to  set  forth  theory  and  practice  in  their  proper  relations, 
and  the  student  is  urged  to  study  the  principles  governing  each 
process  before  passing  to  another  subject.  If  his  mind  is  not 


64  METALLURGY 

clear  on  some  things  included  in  the  preceding  chapters,  he  is  ad- 
vised to  review  until  no  obscurity  remains. 

The  science  of  metallurgy  has  been  written  from  the  accumu- 
lated facts  gained  in  actual  practice,  and  from  that  which  has 
been  borrowed  from  the  fundamental  sciences — mathematics, 
physics,  and  chemistry.  The  great  progress  which  the  metal- 
lurgical industry  has  made  is  due  to  the  study  and  perseverance  of 
scientific  and  practical  men.  Many  of  the  problems  which  seem 
so  simple  now,  were  extremely  difficult  to  solve,  and  the  solution 
came  only  after  long  and  painstaking  experiments. 

The  field  of  metallurgy  is  a  fruitful  one  for  the  inventor.  It 
has  offered  subjects  for  research  to  men  of  every  age,  and  much 
still  remains  to  be  discovered.  The  man  with  native  ability  and* 
scientific  training  is  the  best  equipped  for  conducting  metallurgi- 
cal processes  and  enterprises. 


CHAPTER   VIII 


IRON— ORES  AND  PROPERTIES 

History. — Iron  is  a  prehistoric  metal.  So  far  as  there  is  any 
evidence  the  Egyptians  and  Assyrians  were  the  first  to  become 
acquainted  with  the  properties  of  iron,  and  to  devise  a  process  for 
smelting  it.  Pieces  of  iron  have  been  taken  from  the  Egyptian 
pyramids  and  from  other  places,  where  they  are  known  to  have 
remained  for  thousands  of  years.  Other  metals  may  have  been 
more  common  than  iron  with  the  ancients,  on  account  of  the  more 
refractory  nature  of  iron  ores,  but  it  it  quite  likely  that  most  of 
the  very  oldest  specimens  have  been  destroyed  by  natural,  chemi- 
cal processes.  The  Romans  manufactured  large  quantities  of  iron 
during  the  reign  of  Julius  Caesar,  and  the  industry  was  doubtless 
spread  largely  through  Roman  invasion.  England,  Germany  and 
France  have  always  been  the  leading  European  nations  in  the  iron 
trade,  and  the  English  brought  it  to  America.  The  first  iron 
plant  in  America  was  erected  on  the  James  River,  in  Virginia, 
in  1619. 

ORES 

Iron  occurs  as  oxides,  carbonates,  sulphides,  and  native.  Native 
iron  is  found  in  meteorites,  and  as  such  is  only  of  scientific  interest. 
The  oxides  are  by  far  the  most  important  ores  of  iron. 

Oxides. — All  the  common  ores  of  iron  are  included  in  this 
group,  as  are  also  the  richest  ores.  Oxide  of  iron  is  an  ingred- 
ient of  almost  every  soil,  and  as  an  ore  it  is  often  found  in  a  high 
degree  of  purity.  Some  ores  are  more  highly  oxidized  than  others, 
those  containing  the  least  amount  of  oxygen  being  magnetic.  The 
former  are  represented  by  the  general  formula  Fe2O3  and  are 
known  as  hematite,  while  the  latter  are  represented  by  the  formula 
Fe3O4  and  are  known  as  magnetite. 

Hematite. — This  is  the  common  ore  of  iron,  comprising  almost 
entirely  the  great  deposits  of  Lake  Superior  and  the  greater  part 
of  those  of  the  Appalachian  region  and  the  West.     It  occurs  in 
3 


66  METALLURGY 

amorphous  and  granular  masses  and  in  earthy  form,  and  is  de- 
posited in  beds,  veins,  and  pockets.  Hematite  is  usually  without, 
water  of  combination  (anhydrous),  though  some  varieties  are 
hydrated.  The  anhydrous  ores  yield  a  red  powder,  and  the  pow- 
der of  hydrated  ores  is  brown  or  yellow.  Among  the  anhydrous 
ores  are: 

1.  Specular  ore,  occurring  in  crystals  of  metallic  luster  and 
often  iridescent.     It  is  an  important  Lake  ore,  and  very  pure. 

2.  Micaceous  ore,  so  called  from  its  resemblance  to  mica,  is 
often  found  in  glistening  scales  of  great  beauty.     This  is  also  a 
very  pure  ore,  and  is  found  principally  in  the  Lake  region. 

3.  Kidney  ore  occurs  in  small  quantities,  though  often  in  the 
neighborhood  of  large  veins.     It  is  found  in  radiating  masses, 
made  up  with  small,  reniform  or  kidney-shaped  surfaces,  suggest- 
ing the  name.     It  is  frequently  met  with  in  the  Eastern  states. 

4.  Red  Fossil  ore  is  characterized  by  its  being  unctuous  to  the 
touch  and,  in  general,  by  its  red  color.     It  occurs  both  earthy  and 
massive.     Besides  its  importance  as  a  Lake  ore,  red  fossil  ore 
occurs  in  large  quantities  in  the  East  and  South,  being  the  chief 
ore  in  Alabama. 

Of  the  hydrated  oxides  or  brown  hematites  two  varieties  may 
be  noted: 

1.  Limonite,  otherwise  known  as  Ochre  and  Bog  Ore,  occurs 
in  large  quantities  in  the  Eastern  states  and  the  Mississippi  Valley. 
It  is  an  easy  ore  to  smelt,  the  gangue  often  containing  both  silic- 
eous and  calcareous  substances,  making  it  self-fluxing. 

2.  Goethite  is  an  unimportant  ore,  distinguished  from  limonite 
only  in  its  containing  less  water  of  combination. 

Magnetite. — It  is  seen  from  the  formula  (Fe3O4)  that  this  ore 
may  carry  as  much  as  72  per  cent,  of  iron.  When  in  their  purest 
form  the  magnetites  are  the  most  valuable  ores  that  are  smelted. 
In  addition  to  their  magnetic  property,  these  ores  are  distinguished 
by  their  dark  color,  submetallic  luster  and  weight.  They  are  hard, 
massive  and  refractory.  In  this  country  the  chief  deposits  of  mag- 
netite are  in  New  York  and  New  Jersey,  though  it  is  not  infre- 
quently found  with  hematite  in  the  Mississippi  Valley  and  else- 
where. It  is  also  an  important  foreign  ore.  The  famous  de- 


IRON ORES    AND    PROPERTIES  67 

posits  of  Sweden,  probably  the  richest  in  the  world,  consist  mostly 
of  magnetite. 

Carbonates. — These  comprise  a  much  poorer  class  of  ores  than 
the  oxides.  The  highest  content  of  iron  possible,  according  to 
the  formula,  FeCO3,  is  a  little  more  than  48  per  cent.  The  chief 
carbonate  ore  is 

Siderite  or  spathic  iron,  which  is  grayish-white  to  reddish-brown 
in  color,  yields  a  light  colored  powder,  and  is  easily  decomposed 
by  heat  into  the  magnetic  oxide  and  carbon  dioxide.  An  argil- 
laceous variety  of  this  ore  occurs,  usually  in  the  vicinity  of  coal 
deposits,  and  is  known  as  clay  iron  stone.  Carbonate  ores  are  not 
uncommon  in  the  East,  especially  in  Pennsylvania.  They  have  for 
a  long  time  been  the  chief  ores  of  Great  Britain,  though  they  are 
now  becoming  exhausted.  Though  poor  in  iron,  rarely  exceed- 
ing 40  per  cent.,  these  ores  have  been  prized  for  their  freedom 
from  phosphorus,  a  very  objectionable  impurity  in  iron. 

Sulphides. — Attention  is  merely  called  to  the  occurrence  of  iron 
as  sulphide,  the  chief  ores  being  pyrites  (FeS>>),  pyrrhotite 
(Fe~S8)  and  the  magnetic  sulphides.  The  sulphide  ores  are  not 
as  yet  sources  of  iron,  though  large  quantities  are  now  being 
roasted  for  the  recovery  of  sulphur.  If  the  sulphur  can  be  suf- 
ficiently removed  from  the  residues  of  the  roasters,  they  will  be 
utilized  in  this  way,  and  this  seems  possible. 

Some  Impurities  in  Iron  Ores. — Iron  ore  gangue  is  generally 
acid  in  character,  the  bases  alumina,  lime,  magnesia,  etc.,  being 
insufficient  to  neutralize  the  silica.  Sulphur  and  phosphorus  are 
deleterious  elements  often  encountered,  and  in  rare  cases  arsenic 
is  present.  Manganese  is  contained  in  almost  all  iron  ores,  its 
presence  being  rather  desirable.  Titanium,  chromium  and  zinc 
are  not  uncommon  impurities.  In  some  instances  these  metals 
have  so  far  replaced  the  iron  as  to  justify  a  special  name  for  the 
ore.  The  mineral  ilmenite,  for  example,  contains  a  mixture  of 
ferric  and  ferrous  oxides  with  the  dioxide  of  titanium.  The 
best  known  American  deposits  of  high  titanic  iron  are  in  New 
York.  Chromite,  the  sesquioxide  of  chromium  mixed  with  fer- 
rous and  ferric  oxides,  is  another  well  known  and  very  valuable 
compound  ore.  Chrome-iron  ore  occurs  at  various  points  in  the 


68  METALLURGY 

United  States  in  small  quantities,  but  this  country's  supply  is 
drawn  chiefly  from  abroad.  A  more  remarkable  mixed  ore  oc- 
curs in  New  Jersey,  known  as  Franklinite.  It  contains  three 
metals,  iron,  manganese  and  zinc  in  workable  quantities. 

Dressing. — The  larger  part  of  iron  ores  smelted  in  the  United 
States  are  exceptionally  pure,  and  require  no  preliminary  treat- 
ment. In  foreign  countries  a  much  larger  percentage  of  the  ores 
requires  some  kind  of  treatment,  and  there  are  few  ores  that  could 
not  be  improved  for  the  smelter  by  a  concentrating  process.  Car- 
bonate ores,  and  those  containing  a  high  percentage  of  moisture 
may  be  profitably  calcined ;  those  containing  sulphur,  roasted ; 
coarse  ores  containing  much  gangue,  washed ;  and  fine  ores,  con- 
centrated with  magnetic  machines.  Many  of  the  ores  of  the 
Eastern  and  Southern  states  are  concentrated  by  the  latter  meth- 
ods, roasting  being  occasionally  resorted  to. 

PROPERTIES 

Pure  Iron. — Iron  is  grayish  white  in  color  and  highly  lustrous. 
The  specific  gravity  is  7.8  and  the  fusion  point  is  about  i,6oo°C. 
It  is  remarkably  tough,  malleable  and  ductile,  and  its  tensile 
strength  is  about  30,000  pounds  per  square  inch.1  Iron  possesses 
the  property  of  magnetism  to  a  higher  degree  than  any  other 
metal.  Iron  welds  readily,  can  be  welded  to  a  few  other  metals, 
and  will  form  alloys  with  most  all  metals.  While  in  the  molten 
state  iron  occludes  oxygen,  nitrogen  and  other  gases  which  may 
be  in  contact  with  it. 

Pure  iron  is  a  very  uncommon  article  of  commerce,  though 
there  are  some  grades  which  contain  so  little  foreign  matter  as 
to  possess  properties  approximately  the  same  as  those  above  noted. 
Since  the  properties  of  a  metal  are  governed  by  its  composition 
and  by  heat  and  mechanical  treatment,  the  possibility  of  develop- 
ing or  improving  these  properties  is  readily  seen.  In  no  metal 
has  this  been  realized  to  so  great  an  extent  as  in  iron.  Within 
certain  limits,  by  alloying  or  combining  other  elements  with  iron 
in  varying  proportions,  a  metal  of  any  desired  property  may  be 
produced.  Hence  has  arisen  the  great  variety  of  commercial 
irons,  each  designed  for  specific  purposes.  A  knowledge  of 
1  Roberts- Austen's  Metallurgy. 


IRON ORES    AND    PROPERTIES  69 

the  effect  of  impurities  is  indispensable  to  iron  manufacturers. 

Effects  of  Other  Elements  on  the  Properties  of  Iron. — It  is  im- 
possible to  state  accurately  and  completely  the  effect  of  the  var- 
ious elements  found  in  iron — a  full  and  systematic  research  has 
never  been  made.  The  only  way  to  gain  full  information  on  this 
subject  would  be  to  add  the  elements  to  iron  separately  and  in 
varying  proportions,  and  then  to  test  each  product.  This  would 
be  an  exceedingly  laborious  task,  which  the  end  would  not  justify. 
Since  the  effect  of  any  ingredient  is  influenced  more  or  less  by  the 
presence  of  others,  and  since  commercial  iron  usually  contains  a 
number  of  foreign  elements,  the  information  is  for  the  most  part, 
drawn  from  tests  made  on  the  several  grades  as  manufactured. 

The  principal  non-metallic  elements  combined  in  iron  are  car- 
bon, silicon,  sulphur,  phosphorus  and  oxygen. 

Carbon. — When  practically  free  from  other  elements  molten 
iron  may  be  made  to  dissolve  as  much  as  4.63  per  cent,  of  its  own 
weight  of  carbon.1  On  cooling  some  of  this  carbon  is  retained 
in  combination  with  the  iron,  while  the  rest  separates  in  scale- 
like  crystals  of  free,  graphitic  carbon.  Some  of  this  graphitic 
carbon  escapes  during  the  cooling,  but  the  larger  part  of  it  is  in- 
corporated in  the  mass  of  solidifying  metal.  Graphite  obtained 
from  pig  iron  is  called  "kish."  That  in  the  iron  may  easily  be 
detected  with  the  eye  on  a  fractured  surface.  If  the  molten  iron 
be  cooled  slowly  the  greater  part  of  the  carbon  will  separate  in  this 
way,  while  in  rapid  cooling  the  crystals  do  not  have  time  to 
grow,  and  most  of  the  carbon  is  retained  in  the  combined  form. 
Although  the  saturation  point  for  total  carbon  in  iron,  as  deter- 
mined by  experiment,  is  4.63  per  cent.,  it  is  rare  that  iron  is  made 
to  contain  more  than  3.50  per  cent.,  unless  some  other  substance 
is  present,  which  raises  the  saturation  point.  The  saturation  point 
may  be  either  raised  or  lowered  by  the  presence  of  other  elements. 

Graphitic  carbon  imparts  to  iron  a  dark-gray  color,  furnishing 
a  most  ready  means  of  detection.  It  renders  the  fracture  coarse 
and  rough,  presenting  the  faces  of  graphitic  scales,  often  one- 
fourth  inch  across.  These  destroy,  to  a  large  extent,  the  con- 
tinuity of  the  metal,  impairing  its  strength.  The  tenacity,  elastic- 
1  See  Howe's  Metallurgy  of  Steel,  p  .5. 


7O  METALLURGY 

ity,  toughness,  malleability  and  ductility  are  checked  or  suppressed. 
The  hardness  is  not  much  altered;  the  fusion  point  is  lowered, 
and  welding  is  made  difficult  or  impossible.  The  presence  of 
graphitic  carbon  in  iron  prevents  to  a  large  extent  the  occlusion 
of  gases,  and  is  often  desirable.  It  is  rarely  found  in  any  other 
than  cast  iron.  Those  containing  a  high  percentage  of  graphitic 
carbon  are  known  in  commerce  as  "gray  irons." 

Combined  carbon  exerts  a  more  profound  influence  upon  the 
properties  of  iron  than  that  of  any  other  element.  The  relation 
of  carbon  to  iron  has  been  studied  exhaustively  from  both  the 
scientific  and  practical  points  of  view.  The  fracture  of  carbon 
iron  varies  from  fibrous  or  hackley  (the  fracture  of  pure  iron) 
to  fine  granular  (the  fracture  of  high  carbon  steel).  So  marked 
is  this  effect  in  iron  which  does  not  contain  interfering  elements, 
that  an  experienced  observer  can  estimate  the  carbon  to  within  a 
few  hundredths  per  cent.,  from  the  appearance  of  the  fracture. 
The  effect  of  combined  carbon,  in  general,  is  to  increase  ten- 
acity, elasticity,  and  hardness.  The  maximum  tensile  strength, 
and  the  highest  limit  of  elasticity  are  gained  with  about  one  per 
cent,  of  carbon.  The  hardness  is  increased  by  adding  carbon  until 
the  saturation  point  is  reached.  At  this  point  iron  is  so  brittle  that 
it  can  be  powdered.  Carbon  lowers  the  fusion  point,  and  inter- 
feres with  welding.  Iron  containing  a  high  percentage  of  car- 
bon can  not  be  welded.  High  carbon  iron  is  employed  for  mak- 
ing "permanent  magnets",  since  on  being  magnetized,  it  retains 
the  property  indefinitely.1  Besides  being  influenced  by  the  pres- 
ence of  other  elements,  the  effect  of  carbon  is  governed  by  heat 
treatment.  It  is  believed  that  carbon  forms  a  number  of  definite 
compounds  with  the  iron  in  which  it  has  been  dissolved,  the  com- 
position of  these  varying  with  the  amount  of  carbon  present,  the 
heat  conditions,  etc.,  and  that  these  carbides  determine  the  pro- 
perties of  the  iron.  The  probable  number  of  carbides  and  their 
formulas  are  unsettled  questions,  but  there  is  sufficient  evidence 
of  their  existence.  The  carbide,  Fe3C,  has  been  isolated,  and  an- 
other, having  approximately  the  formula,  Fe2C,  is  supposed  to 

1  The  permanency  and  efficiency  of  steel  magnets  is   increased  by  add- 
ing carbon  up  to  0.85^  (Metcalf). 


IRON — ORES   AND    PROPERTIES  7! 

exist.  Two  forms  of  carbon  are  generally  recognized  by  the  pro- 
perties which  they  impart  to  iron.  Cement  carbon  takes  its  name 
from  the  fact  that  it  enters  and  migrates  through  unfused  iron  by 
a  process  known  as  cementation.  The  "cement  bars/' made  by  this 
process,  furnish  the  best  example  of  the  existence  of  this  carbide. 
It  is  the  same  that  was  first  isolated  by  Abel  and  assigned  the 
formula  Fe3C,  and  is  the  principal  carbide  in  annealed  steels.  The 
effect  of  cement  carbon  is  to  increase  the  tensile  strength  of  iron. 
Another  form  known  as  hardening  carbon,  the  composition  of 
which  is  undetermined,  is  found  in  high  carbon  irons,  especially 
those  which  have  been  cooled  suddenly.  If  iron  containing  cement 
carbon  is  heated  to  redness  and  quenched,  that  carbide  is  de- 
composed into  one  containing  more  carbon,  and  iron  is  liberated. 
The  physical  effect  is  that  the  iron  is  hardened.  Ledebur  states 
that  hardening  carbon  is  formed  when  iron  is  quenched  from  a 
temperature  of  200°  C.  In  addition  to  this,  its  most  marked 
effect,  hardening  carbon  promotes  tenacity  and  elasticity  in  iron 
and  lengthens  the  duration  of  magnetism.  For  a  further  study  of 
the  relation  of  carbon  to  iron  see  p.  165. 

Silicon. — Like  carbon,  silicon  may  exist  in  iron  in  both  the  free 
and  the  combined  state.  Free  silicon,  however,  separates  only 
under  peculiar  conditions,  and  is  rarely  met  with.  It  combines 
with  iron,  probably  in  several  proportions,  and  the  silicon-iron 
compounds  are  readily  absorbed  in  molten  iron.  Rich  alloys  or 
mixtures  containing  from  5  to  15  per  cent,  of  silicon  are  manu- 
factured under  the  name  of  ferro-silicon.  The  silicon-iron  com- 
pounds are  readily  absorbed  in 'molten  iron.  Iron  is  rarely  made 
to  carry  more  than  four  per  cent,  of  silicon.  The  fracture  of 
silicon  irons  is  bright  and  crystalline,  becoming  coarser  as  the 
silicon  is  increased.  In  the  purer  forms  of  iron  silicon  is  an  ob- 
jectionable element,  its  tendency  being  always  toward  weakening 
the  metal  and  rendering  it  hard,  brittle  and  unworkable.  It  lowers 
the  fusion  point  and  checks  occlusion.  It  is  sometimes  added  to 
iron  when  it  is  cast  to  increase  soundness  (see  p.  158).  An  in- 
crease of  silicon  in  cast  iron  is  attended  with  a  greater  separa- 
tion of  graphite. 

Sulphur. — This  element  is  found  in  all  grades  of  iron  except 


72  METALLURGY 

that  made  from  very  pure  ore,  and  smelted  with  charcoal.  It  ex- 
ists as  FeS,  which  is  readily  dissolved  in  molten  iron.  Sulphur 
is  a  most  objectionable  element  in  the  purer  irons.  A  few  hun- 
dredths  of  a  per  cent,  may  cause  iron  to  crack  while  it  is  being- 
forged  at  red  heat.  This  failing  is  termed  "red  shortness."  The 
effect  of  sulphur  is  less  marked  in  iron  containing  a  high  per- 
centage of  manganese.  The  effect  on  finished  iron  is  not  consid- 
ered serious  if  not  over  0.06  per  cent,  is  present. 

Phosphorus. — The  phosphide  of  iron,  like  the  sulphide,  is  read- 
ily diffused  in  the  metal.  There  are  probably  several  phosphides 
of  iron,  though  their  composition  has  not  been  determined.  Fer- 
ro-phosphorus,  containing  as  much  as  25  per  cent,  of  phosphorus 
is  now  manufactured.  In  the  purer  irons  phosphorus  is  a  dan- 
gerous ingredient.  The  metal  containing  it  may  be  quite  easily 
forged,  showing  no  sign  of  weakness  while  hot,  but  when  cold  the 
toughness,  malleability  and  ductility  are  impaired.  As  much  as 
half  a  per  cent,  would  render  iron  very  brittle  when  cold,  though 
it  shows  no  signs  of  failure  while  hot.  Phosphorus  is  practically 
eliminated  from  some  grades  of  iron.  The  highest  grades  of  steel 
made  for  structural  purposes  carry  from  o.oio  to  0.035  Per  cent., 
and  a  great  many  carry  from  0.035  to  o.io  per  cent.  The  effect 
of  phosphorus  is  but  slight  under  0.06  per  cent.  Cast  iron  carries 
from  0.5  to  1.5  per  cent.,  some  phosphorus  being  desirable. 

Oxygen. — The  scale  of  oxide  that  forms  when  iron  is  burnt 
is  not  dissolved  or  diffused  in  the  molten  metal.  A  chemical  analy- 
sis, however,  will  generally  show  in  iron  treated  by  any  refining 
process,  a  small  quantity  of  oxide.  These  mechanically  incor- 
porated particles  weaken  the  metal  in  proportion  to  their  number 
and  size.  If  scale  is  left  on  surfaces  to  be  welded,  it  will  uther 
prevent  the  pieces  from  uniting  altogether,  or  make  the  point  of 
union  weak. 

The  principal  metallic  elements  alloyed  with  iron  are  manganese 
nickel,  chromium,  tungsten,  molybdenum,  vanadium  and  alumi- 
num. 

Manganese. — After  carbon,  manganese  is  the  most  important 
element  that  is  added  to  iron.  It  is  manufactured  for  this  pur- 
pose and  marketed  under  the  names  spiegel-eisen  and  ferro-man- 


IRON — ORES    AND   PROPERTIES  73 

ganese.  These  are  rich  alloys  with  iron,  the  former  containing 
about  25  and  the  latter  about  80  per  cent,  of  manganese.  The 
low  carbon  or  soft  steels  are  made  to  contain  from  0.30  to  0.50 
per  cent,  of  manganese,  and  the  high  carbon  steels  from  0.60  to 
1.25  per  cent.  Manganese  hardens  iron,  but  not  in  the  way  that 
carbon  does.  It  does  not  develop  elasticity  and  tenacity.  As 
much  as  two  or  three  per  cent,  produces  extreme  brittleness. 
When  carbon  and  other  elements  are  present,  the  effect  of  man- 
ganese is  largely  counteracted,  and  its  presence  is  highly  bene- 
ficial.  Thus,  in  cast  iron  it  is  said  to  act  as  a  softener1  and  in  the 
carbon  irons  or  steels  it  may  be  said  to  intensify  the  effect  of  car- 
bon. The  chief  value  of  manganese  lies  in  its  indirect  influence 
upon  the  properties  of  iron.  On  account  of  the  readiness  with 
which  it  diffuses  with  iron,  and  its  stronger  affinity  for  oxygen 
and  sulphur,  it  has  proved  an  excellent  agent  for  the  removal  of 
these  impurities  from  iron,  insuring  at  once  soundness  and  free- 
dom from  red-shortness. 

If  more  than  seven  per  cent,  of  manganese  is  added  to  iron, 
remarkable  toughness  and  hardness  are  developed.  The  famous 
Hadfield  steels  contain  about  13  per  cent,  of  manganese,  and  are 
at  once  so  tough  and  so  hard  that  they  can  not  be  machined. 

Nickel. — The  extreme  toughness  of  nickel,  its  melting  point, 
and  its  resistance  to  oxidizing  agents  would  seem  to  recommend 
it  as  an  ingredient  in  iron.  Nickel  increases  tenacity  and  elasticity 
in  iron,  and  to  some  extent  hardness.  Welding  is  made  more  diffi- 
cult and  conductivity  is  diminished.  When  the  nickel  is  increased 
beyond  20  per  cent,  the  properties  become  impaired.  The  well- 
known  nickel  steels  contain  about  three  per  cent,  of  nickel.  Larg- 
er quantities  are  sometimes  added  to  iron  to  render  it  non- 
corrodible. 

Chromium. — This  metal  is  manufactured  chiefly  from  chrome- 
iron  ore  which  yields  an  alloy  (ferro-chromium)  containing  up- 
wards of  65  per  cent,  of  chromium.  In  this  form  it  is  added  to 
steel  to  improve  its  wearing  and  cutting  power.  The  tensile 
strength  and  elastic  limit  are  raised  in  iron  by  the  presence  of  chro- 
mium. In  pure  iron  the  hardness  is  not  much  affected,  but  high 
1  Turner's  Metallurgy  of  Iron,  p.  205. 


74  METALLURGY 

carbon  iron  with  two  per  cent,  of  chromium  is  harder  than  any 
carbon  iron.  It  is  believed  that  the  extreme  hardness  of  chrome 
steels  is  due  to  the  fact  that  chromium  raises  the  saturation  point 
of  iron  for  carbon,  the  alloy  holding  more  carbon  in  the  harden- 
ing form  than  it  is  possible  for  iron  alone  to  hold.  Chrome 
steel  is  readily  forged  though  difficult  to  weld. 

Chrome-nickel  steel  is  manufactured,  combining  the  properties 
of  chromium  and  nickel  steels. 

Tungsten. — The  use  of  this  metal  is  more  limited,  it  being  much 
rarer  than  either  of  the  last  two.  Ferro-tungsten  is  prepared  from 
wolframite,  and  contains  a  high  percentage  of  tungsten  (about 

75  per  cent.).     The  metal  is  usually  added  to  iron  in  this  form. 
Like  chromium,  tungsten  exerts  no  remarkable  influence  upon  the 
properties  of  iron  except  in  the  presence  of  carbon.  When  alloyed 
with  high  carbon  iron,  hardness  is  developed,  which  may  exceed 
even  that  of  chrome-steel.     Tungsten  steels  are  known  as  "self- 
hardening,"  because  they  do  not  require  tempering.     Tungsten 
steels  are  difficult  to  forge  and  can  not  be  worked  at  all  when 
cold.     A  small  percentage  of  tungsten  is  said  to  improve  mag- 
netism in  steel.     The  famous  Mushet  steel  contains  about  two  per 
cent,  of  carbon  and  about  eight  per  cent,  of  tungsten.     Other 
steels  are  made  richer  in  tungsten,  and  are  consequently  harder 
and  more  brittle. 

The  temper  of  steel  that  is  hardened  with  tungsten  is  not  im- 
paired like  that  of  ordinary  carbon  steel  by  heating.  It  appears 
that  the  carbon  is  the  real  hardening  element  and  that  the  action 
on  the  tungsten  is  to  hold  the  carbon  in  solution.  Some  evidence 
of  that  is  found  in  the  following  experiment  which  was  first  ob- 
served by  Langley.  If  a  piece  of  carbon  steel  be  held  against  a 
revolving  emery  wheel  a  shower  of  tiny  stars  of  great  brilliancy 
is  produced,  due  to  the  explosive  combustion  of  the  particles  of 
carbon,  if,  however,  the  steel  contains  three  per  cent,  of  tungsten 
the  sparks  emitted  are  mostly  of  a  dull-red  color,  and  a  red  band 
is  seen  to  cling  to  the  periphery  of  the  wheel. 

Molybdenum  is  similar  to  tungsten  in  its  relation  to  iron. 
About  half  as  much  molybdenum  as  tungsten,  however,  is  re- 
quired to  produce  the  same  result.  In  other  words,  approximate- 


IRON — ORES   AND    PROPERTIES  75 

ly  the  same  result  may  be  obtained  by  adding  tungsten  or  molyb- 
denum to  iron  in  the  ratio  of  their  atomic  weights,  the  atomic 
weight  of  tungsten  being  184  and  that  of  molybdenum  being  96. 
These  metals  are  also  added  together  and  with  chromium  in  iron. 

Vanadium. — The  high  price  of  this  metal  has,  until  recently, 
precluded  any  extended  use  of  it  in  making  alloys  even  for  ex- 
perimental purposes.  Experiments  so  far  indicate  that  vanadium 
strengthens  and  hardens  iron  in  somewhat  the  same  way  that  car- 
bon does  when  but  a  few  tenths  of  a  per  cent,  are  present. 

Aluminum. — It  has  not  yet  been  proved  that  aluminum,  by  its 
direct  action,  develops  any  useful  properties  in  iron.  Its  princi- 
pal use  is  for  removing  oxygen  from  iron  and  for  quieting  "wild 
heats"  of  steel  while  casting.  This,  as  will  be  explained  later, 
is  due  to  the  power  of  aluminum  to  prevent  occlusion. 

Other  Metals. — Titanium,  copper,  tin  and  arsenic  may  occur  as 
impurities  in  iron.  If  present  at  all,  they  usually  amount  to  but 
traces,  and  their  effect  is  not  noticeable.  In  rare  cases,  however, 
large  quantities  of  iron  have  been  ruined  by  these  impurities,  and 
materials  containing  them  in  any  considerable  quantity  are  not 
suitable  for  making  the  ordinary  grades  of  iron. 

Gases. — The  property  of  occlusion,  or  the  solution  of  gases  is 
important  in  the  metallurgy  of  iron.  In  all  processes  wherein 
iron  is  melted,  the  air  or  other  gases  which  come  in  contact  with  it 
will  be  absorbed  to  a  certain  extent.  The  larger  part  of  this  gas 
is  expelled  during  cooling.  Some  separates  in  globules 
("blow-holes")  while  the  metal  is  in  the  semi-solid  con- 
dition, and  that  which  remains  is  held  in  the  metal  as  a 
solid  solution,  i.  e.}  forming  no  visible  cavities,  but  diffusing  or 
alloying  with  the  metal.  As  a  rule,  the  purer  iron  is,  the  less  will 
be  its  solvent  power  for  gases.  Aside  from  the  weakening  effect 
of  blow-holes,  it  is  impossible  to  state  fully  and  accurately  the  ef- 
fect of  dissolved  gases  on  iron.  But  it  is  recognized  in  the  re- 
fining of  iron  that,  other  things  being  equal,  the  best  results  are 
gained  under  those  conditions  which  permit  the  least  amount  of 
occlusion.  It  is  possible  that  many  cases  of  red-shortness  and 
failures  of  various  kinds  in  both  hot  and  cold  iron  are  due  to  oc- 
cluded gases.  Oxygen,  nitrogen  and  hydrogen  gases  are  dis- 


76  METALLURGY 

solved  by  iron,  and  carbon  monoxide  and  carbon  dioxide  are  said 
to  be  dissolved  under  certain  conditions.1  According  to  Percy, 
nitrogen  imparts  to  iron  hardness  and  brittleness,  also  a  brassy 
luster. 

Chemical  Properties  of  Iron. — Iron  combines  with  all  the  non- 
metallic  elements,  generally  forming  two  or  more  distinct  com- 
pounds with  each.  It  is  dissolved  by  all  the  mineral  acids  with 
which  it  forms  well  known  salts.  In  dry  air,  at  ordinary  tempera- 
tures, iron  undergoes  no  change,  but  when  moisture  and  carbon 
dioxide  are  present  it  rusts,  i.  e.,  it  is  slowly  converted  into  a  hy- 
drated  oxide,  approximately  the  same  in  composition  as  some 
hematites.  When  heated  in  the  air  iron  is  converted  into  the 
magnetic  oxide.  In  metallurgy  this  is  known  as  ''scale."  Ferric 
oxide  is  partially  reduced  to  the  magnetic  oxide  by  heat,  and  at  a 
temperature  far  below  its  melting  point  iron  is  reduced  from  its 
oxides  by  carbon,  hydrogen,  and  some  metals  to  the  metallic 
state.  Ferrous  oxide  is  basic  in  character  and  forms  readily  fusi- 
ble compounds  with  silica.  It  may  also  be  made  to  combine  with 
phosphoric  acid  and  other  acid  substances  at  high  temperatures. 
The  oxides  of  iron  are  highly  refractory.  At  a  red  heat  iron  de- 
composes water  into  its  elements,  and  finely  divided  iron  burns 
readily  in  the  air. 


1  Harbord  and  Hall's  Metallurgy  of  Steel,  pp.  612-614. 


CHAPTER  IX 


IRON  SMELTING- CHEMISTRY  OF  THE  BLAST 
FURNACE    PROCESS 

Pig  Iron. — Primitive  methods  for  smelting  iron  employed  tem- 
peratures much  below  its  melting  point  and  wood  or  charcoal  be- 
ing the  fuel  used,  a  soft  and  almost  pure  iron  was  reduced  directly 
from  the  ore.  The  direct  production  of  pure  iron  is  dealt  with 
elsewhere,  it  being  no  longer  practiced  on  the  large  scale.  In 
all  civilized  countries  iron  is  first  prepared  in  the  impure  form 
known  as  pig  iron,  the  purer  forms  being  prepared  from  this  by 
separate,  refining  processes. 

Preliminary  Description  of  the  Blast  Furnace  Process. — The 
drawing  (Fig.  26)  represents  in  section  a  blast  furance,  without 
the  accessory  apparatus.  The  foundation  is  laid  in  concrete  and 
masonry,  and  upon  this  a  circle  of  cast  iron  columns  is  placed  to 
support  the  superstructure.  The  walls  of  the  furnace  above  the 
region  of  the  bosh  are  encased  in  boiler  plates  riveted  together, 
and  the  bosh  walls  are  reenforced  by  heavy  iron  bands.  The  walls 
and  hearth  of  the  furnace  are  thickly  lined  with  fire-brick,  and  in 
the  region  of  the  bosh  and  hearth  the  walls  are  water-cooled.  The 
blast  is  introduced  into  the  furnace  through  a  number  of  openings 
near  the  bottom,  one  of  which  is  shown  in  the  drawing.  The 
bustle-pipe,  which  branches  from  the  blast  main,  surrounds  the 
furnace,  and  to  this  the  pipes  delivering  the  air  into  the  furnace 
(blow-pipes)  are  connected  by  means  of  goose-necks.  The  gases 
are  taken  from  the  furnace  through  one  or  more  openings  at 
the  top.  The  furnace  has  two  hoppers,  the  bottoms  of  which  are 
closed  by  means  of  conical  castings  known  as  bells.  The  bells 
are  hung  on  counterpoised  beams  and  are  lowered  when  the  hop- 
pers are  to  be  emptied.  All  the  older  furnaces  have  but  a  single 
bell  and  hopper.  For  further  descriptions  see  Chapter  X. 

The  components  of  the  blast  furnace  burden  are  the  ore,  flux 
and  fuel,  and  the  air  supply  is  known  as  the  blast  or  the  wind. 


METALLURGY 


Fig.  26. 


IRON   SMELTING  79 

The  gangues  of  iron  ores  in  this  country  are  generally  siliceous, 
and  are  fluxed  with  alumina,  lime  and  magnesia.  Lime  is  gen- 
erally added  as  limestone,  the  other  bases  being  supplied  by  the  ore 
itself  and  by  the  stone  and  fuel.  The  common  fuel  is  coke,  though 
charcoal  and  anthracite  are  used  in  some  localities.  The  blast 
is  heated  in  regenerative  chambers  called  stoves  before  it 
is  delivered  into  the  furnace,  the  combustible  gas  taken  from  the 
top  of  the  furnace  being  utilized  for  this  purpose.  Under  normal 
working  conditions  the  furnace  is  kept  almost  full,  and  the  blast 
is  maintained  at  as  near  a  uniform  temperature  and  pressure  as 
possible.  The  blast,  at  the  moment  it  enters  the  furnace,  reacts 
with  the  fuel  and  is  largely  converted  into  a  reducing  gas,  which 
in  passing  upward  through  the  mass  of  ore,  reacts  with  it  and 
sets  the  metal  free.  The  first  reaction  of  the  blast  with  the  fuel 
together  with  the  initial  heat  carried  in  by  the  former,  creates  a 
very  high  temperature  in  the  bosh  of  the  furnace.  This  facilitates 
the  final  reductions,  the  formation  of  slag  and  the  fusion  of  the 
iron.  The  metal  and  slag,  being  completely  liquidized,  run  down 
into  the  crucible  of  the  furnace,  the  slag  floating  on  the  metal  as 
oil  floats  on  water.  These  are  tapped  out  when  they  have  been 
accumulated  in  sufficient  quantity.  Since  the  ascending  current 
of  gases  is  in  contact  with  coke  all  the  way  to  the  top,  the  gases 
taken  from  the  furnace  are  largely  combustible.  They  are  util- 
ized for  heating  the  blast,  generating  steam,  and  for  other  pur- 
poses. Fine  particles  of  ore,  coke,  etc.,  are  carried  over  with  the 
gases.  This  is  known  as  blast  furnace,  downcomer,  or  flue  dust. 
Chemical  Changes  in  the  Blast  Furnace. — The  reactions  oc- 
curring in  a  blast  furnace  are  exceedingly  intricate,  and  beyond 
the  reach  of  a  thorough  investigation.  The  more  important 
reactions  may  be  known,  and  the  ultimate  changes  can  be  as- 
certained with  exactness  by  an  examination  of  all  the  raw  ma- 
terials and  the  products,  but  the  transitionary  changes  can  not  be 
observed.  Furthermore  the  conditions  existing  in  a  blast  furnace 
can  not  be  reproduced  on  the  experimental  scale,  these  being 
dependent  in  a  measure  upon  the  large  quantities  of  substances 
treated.  The  blast  introduces  the  elements,  oxygen,  nitrogen 
and  hydrogen  into  the  furnace,  the  hydrogen  being  in  a  form 


8O  METALLURGY 

of  water  vapor,  which  is  always  present  in  the  air.  The  action 
of  the  principal  elements  of  the  blast  and  burden  may  be  out- 
lined as  follows  : 

Oxygen.  —  The  oxygen  of  the  blast,  being  already  at  a  high  tem- 
perature, and  cpming  in  contact  with  a  large  excess  of  glowing 
coke,  becomes  saturated  almost  instantly  with  carbon  — 

C  -f  O2  =  CO2 
C  +  CO2  =  2CO. 

Nitrogen.  —  The  nitrogen  of  the  blast  is  for  the  most  part  inert 
and  may  be  said  to  play  no  economic  part  in  the  process.  It  is 
an  interesting  fact,  however,  that  the  conditions  necessary  for  the 
formation  of  cyanide  exist  in  the  blast  furnace.  The  alkali  which 
is  derived  from  the  ash  of  the  coke,  is  reduced  by  carbon,  and 
nitrogen  is  added  — 

K2C03+C4+N2=2KCN+3CO. 

It  has  been  suggested  that  this  reaction  is  responsible  for  the  re- 
duction of  a  large  portion  of  iron,  but  this  would  seem  hardly 
possible  from  the  small  amount  of  cyanide  that  is  known  to  be 
formed. 

'Hydrogen  is  formed  by  the  decomposition  of  water  vapor  as 
in  the  gas  producer.  It  would  seem  to  play  some  part  in  the  re- 
duction of  iron  oxide,  thus  — 

H6+FeA,=Fe2+3H20. 

But  the  water  formed  would  again  be  decomposed  into  steam, 
and  though  this  would  restore  the  hydrogen  for  further  action, 
the  net  result  would  be  a  loss  of  heat,  as  explained  on  p.  42. 

The  principal  solid  substances  in  the  burden  which  enter  into 
the  chemistry  of  the  process  are  carbon,  iron,  manganese,  phos- 
phorus, sulphur,  silicon,  lime,  alumina  and  magnesia. 

Carbon.  —  In  addition  to  the  reactions  with  oxygen,  as  given 
above,  carbon  reacts  directly  with  the  oxides  of  iron,  manganese, 
silicon  and  phosphorus,  reducing  them  completely  — 

Fe,203+C3=Fe2+3CO 


SiO2+Co=Si+2CO 

P205+C5=P2+5CO. 


IRON   SMELTING  8l 

Some  of  the  carbon  enters  into  combination  with  the  iron,  as 
shown  below,  and  a  smaller  portion  is  cemented  into  the  lining  of 
the  furnace,  as  will  be  explained  later. 

Iron. — The  iron  is  almost  completely  reduced  by  the  action 
of  carbon  and  carbon  monoxide.  Where  rich  ores  are  smelted, 
not  more  than  o.oi  per  cent,  of  the  total  iron  in  the  charge  should 
escape  reduction.  The  reduction  begins  with  the  descent  of  the 
ore  and  is  finished  above  the  region  of  the  bosh.  Upon  reaching 
the  bosh  the  iron  is  in  the  form  of  a  spongy  mass  or  a  black 
powder.  It  now  takes  up  carbon,  fuses  and  trickles  down  into 
the  hearth  of  the  furnace.  It  is  at  this  time  that  phosphorus  and 
silicon  combine  writh  the  iron,  and  manganese  is  alloyed  with  it. 
The  small  amount  of  ferrous  oxide  that  is  not  reduced  is  com- 
bined with  silica  in  the  slag. 

Fe20,+3CO=Fe2+3C02 
Fe2O3+CO=:2FeO+CO2 
2FeO+Si02=2FeO.Si02 

Fe  +  C,  +  Si.  +  P.  -f  Mn,  =  Pig  iron. 

Manganese,  which  occurs  in  iron  ores  chiefly  as  the  sesqui- 
oxide  and  the  dioxide,  requires  a  higher  temperature  than  iron 
does  for  its  reduction.  Generally,  about  half  that  is  in  the  ore  is 
reduced,  the  rest  acting  as  a  basic  flux.  Manganese  is  desira- 
ble in  the  blast  furnace  for  its  desulphurizing  effect  on  the  iron. 
The  reduction  of  manganese  is  analogous  to  the  reduction  of  iron. 

Phosphorus  is  completely  reduced  by  carbon,  and  passes  im- 
mediately into  the  iron.  Only  traces  of  phosphorus  are  to  be 
found  in  the  slag.  The  reduction  seems  to  take  place  only  in 
the  hottest  part  of  the  furnace  and  in  the  presence  of  a  large 
amount  of  silica.  Phosphorus  is  present  in  the  raw  materials 
chiefly  as  phosphates  of  iron  and  calcium. 

Sulphur  is  always  present  in  coke  and  not  infrequently  in  iron 
ores  as  pyrite.  A  part  of  this  is  absorbed  by  the  iron  as  the 
monosulphide.  The  larger  part  is  taken  into  the  slag  as  calcium 
sulphide — 

FeS+CaO=FeO+CaS. 

The  conditions  favoring  the  absorption  of  sulphur  by  the  slag 
are  a  high  temperature  of  working  and  a  high  percentage  of 


82  METALLURGY 

bases  in  the  charge.  A  very  liquid  slag  in  large  bulk  naturally 
promotes  the  removal  of  sulphur  from  the  iron. 

Silicon  is  reduced  only  in  the  hottest  part  of  the  furnace,  and 
by  solid  carbon.  The  larger  part  of  the  silica  in  the  charge  re- 
acts witli  lime  and  other  basic  oxides  to  form  the  slag.  The 
silica,  always  retaining  its  two  atoms  of  oxygen,  combines  in 
different  proportions  with  the  bases,  which  are  either  in  the  pro- 
toxide or  the  sesquioxide  state.  These  proportions  are  expressed 
by  the  ratio  of  the  oxygen  in  combination  with  the  base  to  that 
in  combination  with  the  silica.  The  ratio  in  blast  furnace  slags 
is  generally  i  to  I,  or,  representing  the  metal  by  M,  the  general 
formula  for  the  slag  would  be 

(2MO.Si02),     (2M203-3Si02L. 

Lime  and  Magnesia. — These  substances  act  similarly  in  the 
blast  furnace,  the  one  replacing  the  other  in  the  charge.  They 
are  formed  by  the  calcination  of  the  raw  stone,  which  is  usually 
brought  about  'nside  the  furnace — 

CaOO8+MgCO8=CaO+MgO+2CO2. 

A  note  on  the  use  of  previously  burnt  lime  as  a  flux  will  be  found 
on  p.  101.  Lime  is  the  chief  basic  flux  in  the  blast  furnace,  uniting 
with  the  silica  of  the  charge  as  monosilicate.  If  this  ratio  is 
changed  the  slag  becomes  less  fusible,  absorbs  more  heat,  and 
the  temperature  of  the  furnace  is  raised.  The  silicate  of  lime 
alone  is  difficultly  fusible  and  would  not  be  fluid  at  the  tempera- 
ture of  the  furnace  hearth,  but  the  fusion  point  is  lowered  by 
the  presence  of  other  bases,  and  especially  by  alumina. 

Aluminum  is  in  no  wise  reduced,  but  it  enters  into  combina- 
tion with  silica  as  the  sesquioxide  (alumina),  forming  the  mono- 
silicate.  Gredt  has  found  that  a  mixture  of  alumina,  lime  and 
silica  is  most  fusible  when  the  proportion  is  1.07  parts  A12O3, 
1.75  parts  CaO,  and  1.87  parts  SiCV 

Other  Metals. — The  metals  titanium,  zinc,  copper,  arsenic  and 
chromium  are  sometimes  present  in  blast  furnace  charges  in 
sufficient  quantity  to  affect  the  working  of  the  furnace  or  the 
quality  of  the  iron  produced. 

Titanium  is  scarcely,  if  at  all,  reduced,  unless  present  in  con- 
1  Stahl  und  Eisen,  9,  756. 


IRON   SMELTING  83 

siderable  quantity.  Being  a  highly  refractory  substance,  titanic 
oxide  may  render  the  slag  difficult  to  fuse,  unless  the  proper 
mixtures  are  used  in  the  charge  to  flux  it.  High  titanic  ores 
have  been  smelted  successfully  in  blast  furnaces  by  allowing  the 
titanic  oxide  to  replace  silica  in  the  slag.1  An  interesting  com- 
pound of  titanium  with  carbon  and  nitrogen,  known  as  cyano- 
nitride  of  titanium,  is  often  found  in  the  hearth  and  wall  accre- 
tions of  blast  furnaces.  It  is  in  the  form  of  small  cubes,  which 
are  very  hard  and  look  strikingly  like  copper.2 

Zinc,  if  reduced,  does  not  reach  the  hearth  of  the  furnace, 
owing  to  its  volatility.  Any  zinc  vapor  becomes  oxidized  in  the 
cooler  part  of  the  furnace,  probably  by  the  action  of  carbon 
dioxide.  The  oxide  is  deposited  on  the  upper  walls  of  the  furnace 
and  in  the  stoves  and  flues.  Some  enters  the  slag,  rendering  it 
less  fusible. 

Arsenic  is  almost  totally  reduced,  entering  the  iron  as  arsenide 
or  arsenate. 

Copper  is  reduced  and  alloyed  with  the  iron.- 

Chromium  is  more  difficult  to  reduce  than  iron,  but  it  may  be 
reduced  in  considerable  quantity  if  a  high  temperature  is  em- 
ployed. Owing  to  the  refractory  nature  of  chromium  oxide, 
special  fluxes  are  required  for  smelting  chrome-iron  ores  in 
blast  furnaces. 

Blast  Furnace  Slag. — It  is  seen  from  the  foregoing  that  blast 
furnace  slag  is  a  mixture  of  the  silicates  of  alumina,  lime  and 
magnesia,  the  silicates  of  iron,  manganese  and  other  bases  being 
present  in  smaller  quantities,  or  as  impurities.  Sulphur  is  pres- 
ent, chiefly  as  sulphide  of  calcium.  It  has  also  been  shown  that 
the  composition  of  slags  varies  with  that  of  the  raw  materials 
and  with  the  temperature  at  which  they  are  formed.  Otherwise 
expressed,  the  slag  is  an  indicator  of  the  condition  of  the  fur- 
nace. Some  idea  of  the  composition  of  a  slag  may  be  gained 
from  its  viscosity  while  fused  and  from  its  appearance  after 
cooling.  For  example,  a  slag  of  the  proper  composition  will  flow 
neither  too  sluggishly  nor  too  readily,  but  in  a  manner  well 

1  Paper  on  the  smelting  of   titaniferous  ores  by   A.   J.   Rossi.   Trans. 
Amer.  Inst.  Min.  Eng.,  21,  832. 

2  Percy,  "  Iron  and  Steel,"  pp.  163,  510. 


84  METALLURGY 

known  to  the  trained  observer.  Too  much  silica  in  the  slag  will 
be  indicated  by  free  flowing,  and  too  much  lime  by  the  reverse. 
The  fracture  of  a  high  silica  slag  is  glassy,  while  a  limey  slag 
presents  a  granular  fracture  with  a  dull-gray  color.  Siliceous 
or  "lean"  slags  are  apt  to  contain  a  good  deal  of  iron,  which 
may  render  them  dark-brown  in  color,  or  even  black.  If  much 
manganese  is  present  the  color  will  be  green.  A  siliceous  slag 
indicates  that  the  furnace  is  working  at  a  low  temperature,  and 
the  iron  is  likely  to  be  high  in  combined  carbon  and  high  in  sul- 
phur. No  fixed  rule  can  be  laid  down  for  these  indications,  since 
the  condition  of  the  furnace  is  subject  to  irregularities,  the  effect 
of  which  on  the  product  is  indeterminable. 

TYPICAL  BLAST  FURNACE  SLAG. 

SiO2         A12O3          MnO          FeO          CaO  MgO          CaS  P2O5        K2O,  TiO2,  etc. 

43        14-50          i          0.25        34  3.50         2  0.05  2.70 

Wall  Accretions. — Particles  of  coke,  lime,  ferrous  oxide  and 
other  refractory  substances  are  agglomerated  and  cemented  to  the 
walls  of  the  furnace  by  a  slag.  The  deposited  material  increases 
to  some  thickness  and  forms  a  protective  coating  over  the  lining. 
It  extends  all  the  way  from  the  upper  limit  of  fusion  in  the  fur- 
nace to  the  crucible,  its  composition  varying  with  the  conditions 
at  different  heights.  Aside  from  the  beneficial  result  of  wall 
accretions,  there  is  danger  of  an  irregular  growth  on  the  walls 
of  blast  furnaces.  The  accretion  may  extend  inward  for  a  con- 
siderable distance  around  the  furnace  and  form  a  "scaffold." 
With  this  as  a  starting  point  the  stock  may  arch  above  the  melt- 
ing zone  and  hang  for  some  time.  This  is  followed  by  a  "slip," 
which  is  the  falling  and  settling  of  the  burden.  This  upsetting 
of  the  furnace  burden  is  a  most  undesirable  occurrence,  being 
specially  disastrous  to  the  working  of  tall  furnaces.  Hanging 
and  slipping  are  not,  however,  always  to  be  attributed  to  wall 
accretions.  Abnormal  accretions  or  scaffolds  are  less  likely  to 
form  in  furnaces  that  are  charged  and  blown  with  regularity 
and  in  which  regularity  of  working  is  aided  by  an  even  distribu- 
tion of  the  stock.  Accretions  may  be  removed  by  increasing  the 
temperature  at  that  point.  This  may  be  done  by  introducing  a 
special  tuyere  or  injecting  oil  in  the  region  of  the  obstruction. 


IRON   SMELTING  85 

Blast  Furnace  Gas. — The  composition  of  blast  furnace  gas  is 
about  the  same  as  unenriched  producer  gas,  the  conditions  under 
which  it  is  formed  being  similar.  The  analysis  here  given  may 
be  taken  as  typical  for  gas  from  a  coke-burning  furnace. 

Nitrogen        Carbon  dioxide        Carbon  monoxide         Carburets         Hydrogen 
60  14  24  II 

The  gas  also  contains  small  amounts  of  sulphur  compounds,  water 
vapor  and  fine  particles  of  solid  matter. 


CHAPTER  X 


IRON  SMELTING— THE  BLAST  FURNACE  PLANT 
AND  PROCESS 

Description  of  the  Plant. — The  principal  parts  of  a  blast  fur- 
nace plant  are  outlined  in  the  elevation  (Fig.  27).  Referring  to 
the  numbers,  I  is  the  furnace  and  2  the  regenerative  stoves  for 


Fig.  27. 


heating  the  blast.  The  down-take,  3,  conducts  the  gas  from  the 
furnace  to  the  dust  catcher,  5.  The  small,  vertical  pipes,  4,  are 
called  "bleeders."  They  are  fitted  with  relief  doors  at  the  top 
to  allow  gas  to  escape  when  the  pressure  exceeds  a  certain  limit. 


IRON   SMELTING  / 

From  the  dust  catcher  the  gas  is  conducted  to  the  stoves  through 
the  main,  6.  A  part  of  the  gas  is  burned  in  the  stoves  and  the 
remainder  is  burned  under  boilers.  The  cold  blast  is  brought 
from  the  blowing  house  in  the  main,  7.  The  blast  is  let  into  the 
stoves  in  turn  by  means  of  control  valves.  After  passing  through 
one  of  the  stoves  the  air  is  conducted  to  the  furnace  in  the  hot 
blast  main,  8.  The  products  of  combustion  from  the  stoves  enter 
the  tunnel,. 9,  which  leads  to  the  tall  chimney,  10.  The  gate 
valves  controlling  the  entrances  to  the  tunnel  are  outlined  in  the 
drawing.  The  hot  blast  and  gas  valves  are  on  the  other  side  of 
the  stoves,  n  shows  the  outline  of  the  casting  shed,  and  12  the 
skip  car  for  hoisting  the  material. 

The  Furnace  Stack. — The  drawing  on  p.  78  shows  the  lines  of 
a  typical  American  furnace.  The  quality  of  the  ore  and  fuel 
and  the  output  are  governing  points  in  the  construction  of  blast 
furnaces.  A  furnace  that  is  rather  low  (not  over  75  feet)  and 
wide  at  the  bosh  seems  to  be  most  suitable  for  smelting  lean 
ores,  since  it  affords  a  high  temperature  and  a  large  melting 
area  in  that  region.  Tall  stacks  (such  as  the  drawing  represents) 
are  suitable  for  rich  ores  and  are  necessary  to  the  greatest  yields 
of  iron.  As  large  producers  of  iron,  they  require  a  firm  coke,  to 
withstand  the  weight  of  the  burden  and  a  high  pressure  of  blast. 
The  well  or  crucible  of  a  furnace  with  a  high  stack  is  made 
larger  in  proportion,  and  the  bosh  walls  are  made  steeper,  for 
the  reduction  and  fusion  zones  are  higher  than  in  low  stacks, 
and  the  burden  is  thus  made  to  descend  more  rapidly. 

While  building  a  furnace  some  special  precautions  are  taken  in 
constructing  the  bosh  walls.  These  are  subjected  to  greater  wear 
from  the  stock  than  the  upper  walls,  since  their  slope  is  out- 
wards, and  with  the  higher  temperature  and  scouring  slag  they 
are  more  rapidly  fluxed  away.  The  life  of  the  bosh  walls  is 
greatly  lengthened  by  water  cooling.  This  is  accomplished  by 
introducing  hollow  blocks  of  cast  iron  or  bronze  into  the  walls, 
in  the  manner  shown  in  Fig.  28,  and  causing  water  to  circulate 
through  these.  The  hearth  of  the  furnace  is  cooled  by  allowing 
the  water  which  is  discharged  from  the  coolers  to  circulate  in  a 
trench,  which,  surrounds  the  furnace  at  the  base.  Gayley's  bosh- 


88 


METALLURGY 


SCOTT'S  PATENT  BOSH  PLATE. 


Fig.  28— Showing  Arrangement  of  Cooling  Plates  and  Tuyeres. 
(Best  Manufacturing  Co.) 


IRON    SMELTING 


89 


cooling,  bronze  plate  is  represented  by  Fig.  29.  The  water  is 
admitted  through  one  of  the  openings  and  discharged  through 
the  other,  having  but  the  one  course.  The  webs  inside  the  plate 
permit  of  its  being  made  light  without  danger  of  crushing  in  the 
furnace  wall.  The  plate  is  cast  smooth  on  the  top  and  bottom 
and  is  wedge-shaped,  so  that  it  can  easily  be  inserted  in  the  fur- 
nace wall  or  removed  when  renewal  is  necessary. 

The  tuyeres,  or  openings  through  which  the  blast  enters,  are 
also  water-cooled.  The  general  arrangement  is  shown  in  Fig. 
30.  The  tuyere,  into  which  the  blast  pipe  is  fitted,  projects  through 


Fig.  29 — Gayley  Plate.     (Best  Manufacturing  Co.) 

the  wall  of  the  furnace  to  the  interior,  as  shown  in  Figs.  26  and 
28.  The  tuyere,  in  turn,  fits  into  the  larger  cooler  in  the  manner 
shown.  The  large  cooler  is  a  protection  to  the  brick  work,  since 
it  does  not  have  to  be  renewed  often,  and  in  drawing  and  insert- 
ing tuyeres  the  bricks  are  not  disturbed.  Water  is  circulated 
through  the  tuyere  and  cooler  by  means  of  separate  supply  and 
waste  pipes. 

The  number  and  size  of  the  tuyeres  is  largely  a  matter  of 
judgment.  Within  certain  limits,  the  fewer  the  number  of  tuy- 
eres and  the  larger  their  diameter,  the  greater  will  be  the  pene- 
trating power  of  the  blast,  while  with  a  larger  number  of  tuyeres, 
the  blast  is  more  evenly  distributed.  The  number  of  tuyeres  at 
different  furnaces  varies  from  8  to  16,  12  being  common. 


METALLURGY 


Charging  Apparatus. — At  the  older  plants  the  stock  is  raised 
to  the  level  of  the  furnace  top  by  means  of  elevators  or  platform 
hoists,  the  materials  having  been  loaded  into  barrows  and 
weighed,  and  from  these  it  is  wheeled  by  laborers  and  dumped 
into  the  furnace  hopper. 

The  modern  blast  furnace  charging  apparatus  consists  of  the 
bell  and  hopper  (Fig.  26),  and  often  a  special  device  for  dis- 
tributing the  materials  in  the  hopper.  The  materials  are  hoisted 
by  means  of  a  skip  car  or  bucket  traveling  over  an  inclined 
track  from  the  stock  bins  to  the  furnace  top.  From  the  drum 


BOSH    FITTING. 

STYLE  E, 

WITH  UNIVERSAL  UNION  ON  SUPPLY. 
N?l  WITH  THREE  WAY  TUYERE  COCK  AT  C. 
N?2  WITH  Two  WAY  COCK  AT  C. 


Fig.  30. 

of  the  hoisting  engine  on  the  ground  level  a  wire  rope  is  passed 
over  a  sheave  on  the  top  of  the  furnace,  and  fastened  to  the  car. 
At  some  plants  a  double  skipway  with  two  cars  is  employed, 
the  loaded  car  being  hoisted  while  the  empty  is  returning. 

Among  the  first  successfully  operated,  mechanical  hoists  are 
those  of  the  Carnegie  Steel  Company's  furnaces  at  Duquesne, 
Pa.  This  hoist  consists  of  a  bucket  suspended  from  a  truck 
which  traverses  the  track.  The  bucket  is  filled  by  running  in 
the  materials  from  opposite  bins,  thus  effecting  a  good  mixing. 
The  bottom  of  the  bucket  is  closed  by  a  cone  or  bell,  which  can 
be  lowered  to  empty  it.  The  material  is  therefore  not  dumped 


31— Brown  Hoist  and  Distributor.      (Brown  Hoisting  Machinery  Co.) 


IRON    SMELTING  9 1 

but  discharged  around  the  bell  after  the  bucket  has  been  hoisted 
and  placed  in  position  over  the  furnace  hopper. 

With  the  usual  style  of  hoist  the  material  is  dumped  from  one 
side  into  the  hopper,  and  though  it  be  made  to  pass  over  two 
bells,  there  may  be  an  uneven  distribution  leading  to  irregularities 
in  the  working  of  the  furnace.  Stock  distributors  have  been  in- 
troduced to  offset  this  defect.  The  photographic  view  (Fig.  31) 
shows  a  style  of  hoist  and  distributor  invented  by  Alex.  E.  Brown 
of  Cleveland.  It  consists  of  a  conical  hood  or  gas  seal  placed 
over  the  furnace  hopper  and  supporting  the  distributing  hopper 
into  which  the  materials  are  dumped  by  the  skip  car.  The  car 
is  shown  in  the  position  for  dumping,  which  is  done  automatical- 
ly. The  rope  wheel  shown  at  the  top  is  geared  to  the  hopper, 
which  it  revolves  through  a  definite  angle  with  each  return  of 
the  car  to  the  bins.  A  ratchet  arrangement  prevents  the  dis- 
tributor from  turning  in  the  opposite  direction  while  the  car  is 
ascending.  The  distributor  is  a  hopper  or  chute,  terminating 
within  the  hood,  and  provided  with  a  hinged  door  at  the  bottom. 
By  an  arrangement  of  levers  the  door  is  closed  when  the  bell  is 
lowered  to  empty  the  main  hopper.  It  remains  open  while  the 
bell  is  in  the  normal  position.  By  thus  changing  the  position  of 
the  chute  each  car  load  of  material  is  thrown  to  a  different  place 
in  the  main  hopper  and  piling  to  one  side  is  prevented.1 

The  charging  bells  are  hung  on  counterweighted  beams,  and 
are  operated  by  means  of  steam  cylinders  on  the  ground  level. 
The  size  of  the  lower  bell  is  important  in  effecting  the  proper 
distribution  of  the  stock.  If  it  is  too  large  in  diameter  the  ma- 
terial is  thrown  to  the  sides  a§*d  the  lumps  roll  back  to  the  cen- 
ter ;  if  the  diameter  is  too  small  the  material  forms  a  circular  pile 
away  from  the  walls,  causing  the  lumps  to  roll  both  to  the  cen- 
ter and  to  the  walls.2  In  either  case  the  tendency  is  toward  an 
unequal  distribution  of  the  ascending  current  of  gases,  since 
channels  are  at  once  formed  by  the  large  lumps.  Such  condi- 
tions lead  to  irregular  reduction  and  fusion. 

Dust  Catchers. — A  large  part  of  the  dust  that  is  carried  over 

1  Trans.  Amer.  Inst.  Min.  Eng.,  16,  194. 

2  Ibid.,  35,  pp.  224  and  553. 


METALLURGY 


with  the  gases  from  the  top  of  the  furnace  is  detained  by  check- 
ing the  velocity  of  the  current  and  leading  it  abruptly  in  a  dif- 
ferent direction.  A  form  of  dust  catcher  is  shown  in  Fig.  32.  It 


Fig-  32. 

is  a  cylindrical  vessel  with  a  hopper  bottom,  and  provided  with 
an  opening  in  the  bottom  for  letting  out  the  accumulated  dust. 
The  opening  is  closed  by  means  of  a  counterweighted  cone.  The 
vessel  is  constructed  of  boiler  plates  and  lined  with  fire-brick, 
and  is  supported  on  cast  iron  columns.  As  indicated  by  the  ar- 
rows the  gas  enters  the  side  of  the  vessel  and  is  withdrawn  at 


IRON    SMELTING  93 

the  top,  the  head  of  the  outlet  pipe  being  situated  below  the 
center  of  the  chamber.  The  gas  enters  the  chamber  at  a  tangent, 
swirls  around,  and  the  dust  loses  momentum  by  friction  against 
the  walls.  Moreover,  the  current  loses  head  by  reason  of  the 
enlargement  of  the  conduit.  The  dust  settles  in  the  hopper, 
from  which  it  is  removed  periodically.  Other  types  of  dust 
catchers  take  the  gas  in  at  the  top  and  deliver  it  at  the  side,  but 
the  above  type  has  been  found  to  be  more  efficient,  especially 
for  fine  dust.  If  a  more  thorough  cleaning  is  required  the  gas 
is  sprayed  or  led  through  scrubbers. 

Stoves. — The  introduction  of  the  hot  blast  by  Neilson  in  1828 
marked  a  new  era  in  blast  furnace  construction  and  practice. 
While  the  inventor  realized  that  by  heating  the  air  beforehand 
he  could  intensify  the  heat  of  combustion,  his  methods  were 
crude  and  wasteful,  employing  solid  fuel  and  in  no  way  utilizing 
the  waste  gases  from  the  furnace.  Neilson's  invention  led  to 
the  construction  of  many  forms  of  appliance  for  heating  the 
blast,  and  finally  to  the  utilization  of  the  gases,  which  had  be- 
fore been  allowed  to  burn  at  the  top  of  the  furnace.1  Of  the 
earlier  forms  of  blast  heaters  or  stoves,  there  is  but  one  sur- 
vivor in  this  country.  It  consists  of  a  rectangular,  brick  cham- 
ber through  which  the  blast  is  conducted  in  numerous  cast  iron 
tubes.  The  gas  is  burned  in  the  chamber  and  heat  is  trans- 
mitted to  the  blast  through  the  walls  of  the  tubes.  The  very 
high  temperatures  now  carried  in  the  blast  were  never  possible 
with  the  old  style  of  heater,  but  were  attained  after  the  regen- 
erative system  of  firing  was  applied.  The  first  regenerative  stove 
put  into  successful  operation  was  built  by  Cowper  in  1860. 

A  stove  of  the  Cowper  type  is  shown  in  section  in  Fig.  33.  It 
is  essentially  a  fire-brick  chamber,  cylindrical  in  shape,  and  en- 
cased in  iron  plates.  The  combustion  chamber,  C,  is  located  at 
the  side  or  center  and  the  rest  of  the  space  is  filled  with  the 
•division  walls  and  vertical  flues,  F.  The  flues  are  open  at  both 
ends  and  communicate  with  the  combustion  chamber  at  the  top. 
The  space  underneath  the  flues  and  the  combustion  chamber 

1  Aubertot  is  said  to   have  been   the  first  to  utilize  blast  furnace   gas, 
employing  it  for  roasting  ore  in  1814. 


94 


IRON    SMELTING  95 

•communicates  with  conduits  leading  from  the  stove  at  the  base, 
as  shown. 

The  gas  enters  the  stove  through  the  pipe,  G,  air  being  ad- 
mitted for  its  combustion.  The  flame  and  products  of  combustion 
pass  upward  through  C  and  downward  through  the  flues,  F,  and 
heat  is  absorbed  by  the  large  mass  of  brick  work.  The  valve,  Vj, 
being  open,  the  products  of  combustion  pass  into  the  tunnel  or 
flue  by  which  they  are  conducted  to  the  chimney.  When  the 
.stove  has  been  heated  the  gas  is  shut  off,  and  air  is  admitted  from 
the  cold  blast  main  through  the  valve,  V2,  the  chimney  valve  be- 
ing now  closed.  The  air  takes  the  opposite  direction  of  the  gas 
through  the  stove  and  becomes  heated  by  contact  with  the  hot 
bricks.  It  passes  into  the  hot  blast  main  through  the  valve,  V3. 
For  the  management  of  Cowper  stoves  the  following  rules  are 
given  i1 

"To  change  from  gas  to  blast — close  the  chimney  valve;  note 
if  hot  air  comes  out  of  the  air  valve.  If  so,  close  the  air  valve, 
and  if  not,  see  that  the  chimney  valve  is  fully  closed;  then  close 
the  air  valve;  open  the  cold  blast  valve  slowly;  open  the  hot 
blast  valve  quickly." 

"To  change  from  blast  to  gas — close  the  hot  blast  valve;  close 
the  cold  blast  valve  within  bale  until  the  pressure  is  nearly  gone ; 
then  throw  it  wide  open ;  open  the  chimney  valve  fully,  and  then 
open  the  gas  valve." 

Blowing  Engines — The  steam  engine  was  employed  for  blow- 
ing iron  furnaces  soon  after  its  invention.  The  blowing  engine 
was  substituted  for  the  water  blowers  of  medieval  days,  which 
had  replaced  the  ancient  hand  bellows.  The  increase  in  the  size 
and  output  of  blast  furnaces  has  been  dependent  directly  upon 
the  volume  of  air  with  which  they  are  blown.  Since  blast  fur- 
nace possesses  are  generally  the  most  rapid  and  economical  in 
smelting,  the  progress  of  metallurgical  industries  in  general  is 
due  in  no  small  measure  to  the  development  of  blast  apparatus. 
In  operations  requiring  blast  under  but  a  few  ounces  pressure  the 
ordinary  fan  blower  is  used.  For  higher  pressure  a  positive 
blower  is  required,  i.  e.,  one  which  compresses  the  air  until  the 
1  Iron  Age,  47,  i°77- 


96  METALLURGY 

resistance  offered  to  its  passage  is  overcome.  Rotary  blowers 
are  commonly  used  for  small  blast  furnaces,  and  for  large  ones 
reciprocating  blast  engines  are  used.  Engines  which  deliver  the 
air  under  a  pressure  of  more  than  30  pounds  per  square  inch  are 
commonly  called  air  compressors. 

The  engine  shown  in  Fig.  34  is  designed  for  blowing  iron 
furnaces,  Bessemer  converters,  etc.,  and  has  a  capacity  of  30,000 
cubic  feet  of  air  per  minute,  against  a  pressure  of  30  pounds  per 
square  inch.  It  is  of  the  horizontal,  cross-compound  type.  The 
steam  and  air  cylinders  are  placed  tandem,  the  piston  heads  being 
carried  practically  on  a  continuous  rod.  The  engine  is  given 
steadiness  of  motion  by  aid  of  a  large  fly-wheel. 

The  air  cylinders  are  shown  in  the  foreground.  Air  passages 
are  provided  in  the  cylinder  castings,  leading  from  the  middles 
to  the  heads.  The  air  is  admitted  and  discharged  under  the  con- 
trol of  mechanically  operated  valves  on  the  heads  of  the  cylin- 
ders. The  outside  mechanism  of  the  air  valve  gear  is  shown 
on  the  cylinder  to  the  right  in  the  illustration.  The  valves  are 
operated  in  time  with  the  piston  by  means  of  a  wrist  plate,  which 
has  a  bearing  on  the  side  of  the  cylinder.  The  wrist  plate  is 
given  a  slight,  rotary  motion  in  opposite  directions  alternately, 
by  an  eccentric  attached  to  the  main  shaft  of  the  engine.  The 
motion  is  communicated  to  the  valves  by  shafts  on  the  ends  of  the 
cylinder  to  which  the  arms  of  the  wrist  plate  are  attached.  The 
discharge  valves  are  closed  by  plungers  at  the  moment  the  piston, 
in  approaching  them,  reaches  the  end  of  the  stroke.  The  plun- 
gers recede  after  seating  the  valves,  leaving  them  to  be  opened 
automatically  by  the  pressure  of  the  air  in  the  cylinder.  The  in- 
take valves  are  operated  entirely  by  the  mechanism,  their  open- 
ing and  closing  being  timed  with  the  stroke  of  the  piston.  With 
each  stroke  of  the  piston  the  cylinder  is  filled  with  air  from  one 
end  and  emptied  from  the  opposite  end.  Uneven  wear  on  the 
piston  heads  and  cylinders  is  prevented  by  extending  the  piston 
rods  through  the  ends  of  the  cylinders  and  supporting  the 
weight  of  the  pistons  on  slides. 

The  vertical  type  of  blowing  engine  is  in  very  general  use.  It 
has  the  advantage  over  the  horizontal  type  in  taking  up  less  floor 


IRON    SMELTING  97 

space.     The  horizontal  engine,  however,   has  the  advantage  of 
being  more  easily  accessible,  and  is  less  liable  to  vibrations. 

The  gas  engine,  which  has  recently  been  developed  for  indus- 
trial uses,  is  replacing  the  steam  engine  to  a  considerable  extent 
for  blowing  purposes.  A  number  of  large  gas  engines  have  been 
built  by  European  manufacturers,  and  extensive  preparations  are 
being  made  in  this  country  for  their  installation.  It  has  been  de- 
monstrated that  blast  furnace  gas  can  be  used  successfully  for 
running  gas  engines.  The  cleaning  of  the  gas  has  offered  one  of 
the  chief  difficulties  in  using  it,  since  it  is  essential  that  all  dust 
and  grit  be  removed  from  the  gas  before  it  is  introduced  into  the 
cylinders  of  the  engine.  The  cleaning  apparatus  now  in  use  is 
efficient  though  expensive.  The  main  economy  gained  in  the 
conversion  o-f  the  gas  directly  into  mechanical  power  is  in  the 
elimination  of  the  boiler  plant. 

Blowing  In. — The  starting  of  the  blast  furnace  process  is 
known  as  "blowing  in"  the  furnace.  With  a  new  furnace  the 
lining  must  be  thoroughly  dried  and  heated  up  gradually  before 
the  regular,  charging  is  begun.  James  Gayley  has  described  a; 
method  of  blowing  in  furnaces  as  used  at  the  Edgar  Thomson 
Works. 

"In  placing  the  wood  in  the  furnace  the  practice  is  to  support 
on  posts  a  platform  about  two  feet  above  the  tuyere  arch,  and 
under  the  bottom  of  each  post  to  place  a  piece  of  fire-brick  on 
which  is  a  sheet  of  thick  asbestos.  The  wood  is  put  on  in  the 
morning,  the  firing  being  stopped  the  evening  before,  so  that 
the  brick  work  will  be  partially  cooled.  After  the  skeleton  parts 
of  the  scaffold  are  in,  a  charge  of  coke  is  made,  sufficient  to  fill 
the  hearth  up  to  the  bottom  of  the  cinder-notch  opening.  On 
the  platform  planks  are  placed  sufficiently  close  to  prevent  the 
cord  wood  from  falling  through.  Above  the  platform  three 
lengths  of  cord  wood  (hard  wood  is  preferred)  are  placed  on 
end,  with  a  cribbing  in  the  center  to  allow  space  for  the  work- 
men to  pass  up  the  wood.  On  top  of  the  wood  a  blank  charge 
of  250  barrows  of  coke  is  put  in.  With  this  coke  there  is  charged 


98  METALLURGY 

sufficient  limestone  to  flux  the  ash,  and  in  addition  a  few  bar- 
rows of  spiegel-eisen  or  ferro-manganese  slag.  The  regular 
charges  consist  of  12  barrows  of  coke,  12  barrows  of  ore  and 
6  barrows  of  limestone.  The  weight  of  a  barrow  of  coke  is  830 
pounds.  To  the  first  few  charges  an  extra  barrow  of  slag  is 
often  added.  The  space  between  the  scaffold  above  and  the  bed 
of  coke  beneath  is  then  filled  with  kindling  wood,  and  the  fur- 
nace is  ready  for  lighting.  In  addition  to  lighting  the  wood  at 
the  cinder-notch,  red-hot  bars  are  thrust  in  at  each  tuyere  to  start 
the  combustion  uniformly.  When  the  scaffold  has  burned  away, 
allowing  the  stock  to  settle  gently,  and  bringing  hot  coke  or 
charcoal  in  front  of  all  the  tuyeres,  the  blast  is  put  on.  The  time 
from  lighting  to  turning  on  the  blast  varies  from  six  to  ten 
hours.  The  blast  is  put  on  slowly  at  first,  and  increased  hourly 
until  the  volume  of  air  is  one-half  the  normal  quantity,  at  which 
point  it  is  held  until  the  first  cast  of  iron  is  made.  In  order 
to  avoid  explosions,  which  frequently  happen  at  the  start,  the 
valves  in  the  boiler  and  stove  gas  mains  are  closed,  and  all  the 
gas  is  allowed  to  escape  until  after  the  first  cast  is  made." 

Burdening  the  Furnace. — The  furnace  burden  consists  of  a 
number  of  charges,  each  charge  in  turn  consisting  of  weighed 
amounts  of  fuel,  ore  and  flux.  The  charging  is  practically  con- 
tinuous, except  in  case  of  accident  or  other  interruption,  until  tfie 
furnace  is  "blown  out."  The  term  "damping  down"  means  the 
shutting  off  of  the  air  from  the  furnace  and  filling  it  with  coke, 
a  scheme  that  is  resorted  to  when  the  process  has  to  be  sus- 
pended for  a  few  days.  The  furnace  fire  may  be  held  for  a  con- 
siderable length  of  time  in  this  way. 

The  mixtures  for  blast  furnace  charges  can  easily  be  calcu- 
lated from  the  compositions  of  the  materials  to  be  used.  Sup- 
pose, for  example,  that  a  furnace  is  to  be  burdened  for  the  re- 
duction of  1,000,000  pounds  of  iron  in  a  day  of  24  hours,  and 
that  the  daily  burden  is  to  consist  of  100  charges.  Each  charge 
must  then  contain  10,000  pounds  of  iron.  Further,  suppose  that 
the  conditions  require  a  pound  of  coke  for  each  pound  of  iron 
reduced,  and  that  the  analyses  of  the  coke,  ore  and  stone  are  as 
follows : 


IRON    SMELTING 


Mnjt 

SiO2# 

A12O3  + 

CaO* 

MgO* 

0.00 

4.00 

2.00 

O.OO 

O.OO 

I.OO 

18.00 

2.00 

0.50 

0.50 

0.70 

8.00 

3-00 

I.OO 

0.50 

0.40 

3.00 

I.OO 

0.00 

0.00 

0.70 

9.00 

2.40 

0.70 

0.40 

0.00 

5.00 

0.50 

50.00 

I.OO 

Fe  Ibs. 
IOO 

Mn  Ibs. 

Si02  Ibs. 
4OO.OO 

A1203  Ibs. 
2OO.OO 

CaO  Ibs. 

MgO  Ibs. 

9,900 

129.29 

1,662.30 

443.28 

129.29 

73-88 

30 



298.15 

29.82 

2,981.50 

59.63 

10,030 

129.29 

2,360.45 

673.10 

3,110.79 

I33-5I 

Coke i.oo 

Ore  No.  i 45.00 

"         "      2 55.00 

"      "    3 58.00 

"     (Average)1....     53.60 
Stone 0.50 

The  burden  sheet  should  contain,  in  addition  to  the  analyses 

of  the  materials  and  the  number  of  charges,  the  actual  weights 

of  silica  and  bases  in  tabular  form.  The  calculations  are  given 
below. 

Stock  Ibs. 

Coke 10,000 

Ore  Mixture  18,470 

Stone 5,963 

Totals 34,438 

The  10,000  pounds  of  coke  in  the  charge  yields  100  pounds  of 
iron,  leaving  9,900  pounds  to  be  supplied  by  the  ore.  Since  the 
mixture  of  ores  yields  0.536  pound  of  iron  for  each  pound  of 
ore,  the  amount  of  the  mixture  required  is  9,900-^0.536=18,470 
pounds. 

The  weights  of  silica  and  bases  in  the  coke  and  ore  are  now 
computed  and  the  deduction  made  for  self-flux.    Using  the  ratios 
given  on  page  82,  the  weight  of  silica  which  i  pound  each  of 
the  bases  will  flux  is  found  by  the  following  proportions : 
2A12O3  :  3SiO2  :  :  i  :  x  =  0.8823  pound  SiO2 
2CaO  :  SiO2  :  :  i  :x      =  0.5357      "         " 
2MgO  :  SiO2  :  :  i  :  x     =  0.7500      " 

Multiplying  the  weights  of  the  bases  by  these  factors  the  totaJ 
silica  is  found  to  be — 

By  A12OS,  643.28  X  0.8823  =  567.57  pounds  SiO2 

"  CaO,    129.29  X  0.5357  =     69.26       "          " 

"  MgO,     73-88  X  0.75       =    55-41       " 

Total  ==  692.24      " 

The  weight  of  silica  that  remains  to  be  fluxed  by  the  stone  is 
2,062.30 — 692.24=1,370.06  pounds. 

The  fluxing  power  of  the  stone  is  found  by  subtracting  the 
1  NOTE: — The  ores  are  to  be  mixed  in  the   proportions  of   one  part   of 
No.  i,  three  parts  of  No.  2  and  one  part  of  No.  3.     The  average  composition 
is  therefore  computed  on  this  mixture. 


IOO  METALLURGY 

silica  in  I  pound  from  the  total  amount  of  silica  that  would  be 
satisfied  by  the  bases  in  i  pound  of  the  stone — • 

By  A12O3,  0.005  X  0.8823  =  0.00441  pound  Sio2 
"  CaO,    0.50     X  Q-5357  =  0.26785       " 
"  MgO,  o.oi     X  0.75       =  0.00750       "         " 

0.27976 
SiO2  present  —  0.05000      "         " 

Fluxing  power  =  0.22976       "         " 

The  amount  of  stone  needed  is  found  by  dividing  this  factor 
into  the  weight  of  silica  to  be  fluxed — 

1,370.06  -i-  0.22976  ==  5,963 

These  calculations  are  simplified  by  using  the  slide-rule,  pro- 
posed by  Jenkins.1  As  in  most  other  metallurgical  processes, 
more  has  been  learned  about  burdening  blast  furnaces  from  prac- 
tice than  from  theoretical  reasoning.  There  are  times  when  the 
furnace  becomes  irregular  in  its  working,  and  the  burden  must 
be  changed  to  suit  the  conditions.  At  such  critical  times  the 
remedies  lie  entirely  with  the  judgment  of  the  manager. 

The  Fuels  and  Fluxes  of  the  Blast  Furnace  Process. — The  quan- 
tity of  fuel  used  in  the  blast  furnace  is  generally  referred  to  the 
quantity  of  iron  produced.  For  coke  furnaces  the  consumption 
varies  from  1,600  to  3,000  pounds  per  ton  of  iron,  depending 
upon  the  purity  of  the  raw  materials,  the  humidity  of  the  blast  and 
the  general  efficiency  of  the  plant.  It  is  desirable  to  carry  as 
little  coke  as  possible  in  the  burden,  not  only  for  economic  rea- 
sons, but  also  for  the  sake  of  introducing  the  least  amount  of  im- 
purities into  the  iron.  Coke  is  generally  superior  to  most  other 
fuels,  though  the  sulphur  and  phosphorus  it  contains  are  often 
serious  defects.  The  firm,  hard  varieties  of  coke  are  always  pre- 
ferred, since  they  sustain  the  weight  of  the  burden  and  keep 
passages  open  for  the  circulation  of  gases.  The  coke  and  iron 
industries  are  indispensable  to  each  other  and  are  often  con- 
trolled by  the  same  interests.  The  remoteness  of  some  of  the 
great  ore  deposits  in  the  United  States  from  the  supply  of  coke 
has  been  a  hindrance  to  the  growth  of  the  iron  industry,  though 
1  Jour.  Iron  and  Steel  Inst.,  1891,  1,  151. 


IRON    SMELTING  IOI 

it  is  largely  responsible  for  the  wonderful  transportation  facili- 
ties which  now  exist. 

Charcoal  is  still  used  in  some  heavily  wooded  localities  where 
coal  does  not  abound,  as  in  the  Lake  Superior  district.  The  fuel 
consumption  is  lower  in  charcoal  than  in  coke  furnaces.  A 
record  given  by  J.  C.  Ford  of  a  furnace  in  Michigan  shows  an 
average  consumption  of  about  1,630  pounds  to  a  ton  of  iron 
made.1  Charcoal  iron  is  prized  for  its  purity,  though  it  is  not 
made  to  compete  with  ordinary  pig. 

The  use  of  coal  also  continues.  There  are  a  number  of  an- 
tracite  furnaces  in  Eastern  Pennsylvania  still  in  blast,  though 
many  that  were  first  blown  in  with  anthracite  have  since  been 
changed  to  coke.  Anthracite  is  inferior  to  coke  on  account  of 
its  dense  structure  and  its  tendency  to  split  and  crumble  in  the 
furnace. 

The  attempt  has  been  made  to  substitute  gas  for  solid  fuel  in 
the  blast  furnace,  but  without  success. 

Raw  limestone,  in  conjunction  with  alumina,  has  been  found 
to  be  the  most  satisfactory  flux  in  the  blast  furnace.  The  fuel 
consumption  may  be  lessened  by  using  caustic  lime  or  burnt  lime- 
stone, but  when  the  fuel  used  in  burning  the  limestone  and  the 
extra  labor  are  taken  into  account,  there  is  very  little  if  any 
economy.  In  the  low  English  furnaces,  smelting  poor  ores,  there 
seems  to  be  some  advantages  gained  in  the  use  of  lime.2 

Magnesian  limestone  and  dolomite  are  not  uncommonly  used. 
The  prevalence  of  this  character  of  stone  in  the  Lehigh  Valley 
accounts  for  its  usage  in  that  section.  F.  Firmstone  has  shown 
some  results  of  his  experience  with  magnesian  stone.  He  iavors 
its  use,  if  the  alumina  is  kept  low  (below  10  per  cent.),  having 
found  that  the  slag  is  more  fluid  and  that  less  sulphur  passes 
into  the  iron.3 

Management  of  tile  Blast. — The  working  of  a  blast  furnace 
depends  no  more  upon  the  manner  in  which  it  is  burdened  than 
it  does  upon  the  management  of  the  blast.  The  efficiency  of  the 
accessory  apparatus  is  proved  by  the  condition  of  the  blast  in 

1  Jour.  U.  S.  Assoc.  of  Charcoal  Iron  Workers,  8,  272,  274. 

2  Jour.  Iron  and  Steel  Inst.,  1894,  2,  38-57,  and  1898,  1,  69-88. 

3  Trans.  Amer.  Inst.  of  Min.  Eng.,  24,  498. 


102 


METALLURGY 


its  four  phases — temperature,  pressure,  volume  and  humidity. 

Temperature. — The  construction  and  management  of  the  stove 
are  explained  on  pp.  93-95.  Four  stoves  are  generally  built 
with  one  furnace,  the  use  of  this  number  allowing  three  hours 
for  heating  the  brick  work,  if  the  blast  is  kept  on  each  for  one 


t 

2 

3 

, 

Time. 

5 

//»    ^c 

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100 

V          f 

X' 

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r\ 

r\ 

^  _r 

.    r 

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r\ 

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s  r 

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Fig.  3;, 


Fig.  36. 


Fig.  37- 

hour.  Some  blowers  prefer  to  use  two  stoves  at  once  for  heat- 
ing the  blast,  one  having  been  put  on  half  an  hour  before  the 
other.  This  of  course  involves  the  changing  of  stoves  every  half 
hour,  since  the  blast  is  to  be  kept  on  no  stove  longer  than  an 
hour,  but  a  more  uniform  temperature  may  be  maintained  by 
this  method  of  heating.  It  is  the  aim  not  only  to  return  all  the 


IRON    SMELTING  IO3 

heat  possible  to  the  furnace,  but  also  to  keep  the  temperature 
of  the  blast  as  nearly  uniform  as  possible.  By  equalizing  the 
temperature  of  the  blast  there  will  be  less  irregularity  in  the 
working  of  the  furnace.  Equalization  may  be  accomplished  by 
carefully  admitting  air  from  the  .cold  blast  to  the  hot  blast  main 
just  at  the  time  the  stoves  are  changed,  and  gradually  shutting 
off  this  air  as  the  stove  cools  down.  Another  advantage  may  be 
gained  by  this  practice  from  the  fact  that  there  is  aways  a  re- 
serve of  heat  in  the  stoves  which  can  be  drawn  upon  in  case  of 
an  emergency  by  shutting  off  the  cold  air  entirely. 

The  temperature  of  the  blast  is  generally  taken  just  before 
it  enters  the  bustle-pipe.  The  continuous  recording  pyrometer 
has  largely  displaced  the  older  forms,  from  which  only  periodic 
readings  can  be  obtained.  The  average  temperature  carried  in 
the  blast  does  not  much  exceed  750°  C  at  any  furnace.1 

The  pyrometer  records  here  shown  (Figs.  35,  36,  and  37)  are 
from  actual  practice.  The  first  one  shows  regular  heating  of  the 
stoves,  the  temperature  being  taken  from  the  hot  blast  main. 
The  sudden  rise  and  regular  fall  of  the  recording  pen  shows  that 
the  stoves  were  changed  at  the  end  of  every  hour,  but  that  no  at- 
tempt was  made  to  equalize  the  temperature.  At  the  time  of  the 
second  record,  however,  the  temperature  was  leveled  in  the  way 
above  described.  The  third  record  shows  irregular  heating,  due 
to  the  condition  of  the  gas. 

The  above  method  of  leveling  the  blast  temperature  requires 
considerable  skill  and  vigilance  on  the  part  of  the  blower,  and  it 
has  not  proved  entirely  satisfactory.  Several  forms  of  regen- 
erative apparatus  known  as  "equalizers"  have  been  proposed,  but 
their  adoption  does  not  as  yet  seem  probable.  If  adopted  the 
equalizer  will  probably  be  constructed  on  the  principle  suggested 
by  L.  F.  Gjers  and  J.  H.  Harrison.2  They  propose  to  build  an 
additional  stove,  or  a  double  regenerative  chamber,  and  to  lead 
the  hot  blast  in  through  the  checker-work  of  one-half  the  cham- 
ber and  out  through  the  other  half.  The  idea  is  that  the  bricks 
will  absorb  heat  when  the  blast  is  above  the  average  temperature 
and  give  it  back  to  the  blast  when  it  is  cooler  than  the  average. 

1  Turner's  Metallurgy  of  Iron,  pp.  112-114. 

2  Jour.  Iron  and  Steel  Inst.,  1900,  1,  154-162. 


104  METALLURGY 

Pressure. — Increased  pressure  gives  the  blast  greater  pene- 
trating power,  facilitating  more  rapid  combustion  and  conse- 
quently more  rapid  reduction  and  fusion.  There  are  serious  diffi- 
culties in  the  way  of  increasing  the  blast  pressure  beyond  a  cer- 
tain limit,  since  it  would  cause  more  dust  to  be  carried  over  with 
the  gases,  and  would  require  additional  blowing  power  and  better 
construction  throughout  the  entire  system  in  which  the  pressure 
is  to  be  withstood.  The  pressure  at  different  furnaces  varies 
from  8  to  15  pounds.  Furnaces  in  the  Pittsburg  district  not 
uncommonly  carry  15  pounds,  and  some  have  been  made  to  carry 
20  pounds  and  more. 

Volume. — The  rate  at  which  the  furnace  works  is  largely  de- 
termined by  the  volume  of  the  blast.  This  in  turn  is  determined 
by  the  rate  at  which  the  blowing  engines  are  driven  and  the 
capacity  of  the  air  cylinders.  In  practice  the  rate  at  which  the 
engines  are  driven,  i.  e.}  the  number  of  revolutions  the  fly-wheel 
makes  per  minute,  is  recorded  as  expressing  the  volume  of  the 
blast  at  atmospheric  pressure.'  This  does  not  take  into  account 
any  loss  sustained  through  the  working  of  the  intake  valves  and 
leaking  of  the  fittings.  At  the  large  works,  engines  are  em- 
ployed which  can  deliver  as  much  as  25,000  cubic  feet  of  air 
per  minute.  Two  engines  are  generally  used  for  one  furnace. 

Humidity. — The  effect  of  moisture  in  the  blast  upon  the  work- 
ing of  a  furnace  has  long  been  a  subject  of  discussion  among 
metallurgists.  Attention  was  called  to  the  subject  at  a  meeting 
of  British  iron  masters  by  Joseph  Dawson  in  1800. *  It  has  been 
observed  that  furnaces  work  better  in  dry  than  in  wet  weather 
and  that  their  condition  is  apt  to  be  better  in  the  winter  months, 
when  the  humidity  of  the  atmosphere  is  relatively  low,  than  at 
other  seasons.  Taking  the  average  amount  of  moisture  in  the 
air  as  3  grains,  it  is  seen  that  in  a  furnace  taking  2,400,000  cubic 
feet  of  air  per  hour,  in  the  same  time  123  gallons  of  water  must 
be  decomposed.  The  effect  of  this  would  perhaps  not  be  notice- 
able if  it  were  not  for  the  fact  that  the  decomposition  must  take 
place  in  the  bosh  or  melting  zone  of  the  furnace,  any  cooling  of 
which  has  the  most  marked  effect  upon  the  working  of  the  fur- 
1  Reprint  of  Dawson 's  paper  in  Jour.  Iron  and  Steel  Inst.,  1907,  2,  221. 


IRON    SMELTING  IO5 

nace.    The  irregularities  caused  by  changes  in  the  moisture  in  the 
air  are  well  known  to  all  furnace  managers. 

Some  appliance  for  drying  the  air  before  it  is  used  in  the  fur- 
nace has  been  advocated  from  time  to  time,  but  only  recently  the 
problem  seems  to  have  been  successfully  solved.  A  process  look- 
ing to  the  partial  or  ultimate  desiccation  of  air  on  the  large  scale 
has  been  worked  out  under  the  directions  of  James  Gayley.1  Mr. 
Gayley's  first  experiments  along  this  line  were  conducted  at  the 
Lucy  furnace,  in  Pittsburg,  and  the  first  complete  air  drying 
apparatus  is  now  in  operation  in  connection  with  one  of  the  fur- 
naces at  Etna,  near  Pittsburg.  The  method,  as  so  far  used,  con- 
sists in  freezing  the  moisture.  Before  it  enters  the  cylinders  of  the 
blowing  engine  the  air  is  led  through  a  huge  refrigerator — a 
large  chamber  almost  filled  with  the  cooling  pipes.  These  pipes 
are  cooled  by  means  of  ammonia  and  they  expose  a  large  surface 
area  to  the  air.  The  moisture  is  deposited  upon  these  as  frost, 
which  is  removed  after  it  has  accumulated  sufficiently  by  letting 
steam  into  the  pipes.  The  results  gained  after  using  the  dried 
blast  in  the  above  furnace  from  August  25th  to  September  9th 
were  made  public  in  October  of  1904.  These  show  an  increase  of 
25  per  cent,  in  the  output  after  the  application  of  the  dry  blast, 
with  20  per  cent,  decrease  in  the  consumption  of  coke.  These 
figures  were  a  great  surprise  to  metallurgists  both  in  this  country 
and  abroad.  Later  records,  covering  longer  periods  of  time  and 
including  the  winter  months,  show  gains  of  from  10  to  20  per 
cent,  in  the  product  and  an  economy  of  10  to  20  per  cent,  in  the 
consumption  of  coke  by  the  use  of  the  dry  blast.  The  Gayley 
process  is  to  be  used  at  several  of  the  large  plants  in  this  coun- 
try and  in  England. 

Casting. — From  the  position  of  the  tap-hole  (Fig.  26)  it  is 
seen  that  all  the  iron  is  never  tapped  from  the  furnace,  a  residue 
being  left  for  the  protection  of  the  hearth  and  to  prevent  chilling. 
It  is  customary  to  tap  the  iron  six  times  per  day  of  24  hours.  The 
tap-hole  is  kept  closed  with  clay  or  a  mixture  of  clay  and  coke, 
which  has  been  rammed  in  tightly  to  prevent  the  iron  from  break- 

1  For  description  and  illustration  Mr.  Gayley's  invention,  see  Trans. 
Amer.  Inst.  Min.  Eng.,  35,  746.     Supplementary  Paper,  Ibid.,  36,  315. 


io6 


METALLURGY 


ing  out.  The  clay  bakes  into  a  hard  mass,  which  has  to  be 
drilled  through  when  the  furnace  is  to  be  tapped.  After  the  drill 
has  reached  the  softer  interior  a  bar  is  driven  through  and  the 
iron  flows  out  when  this  is  withdrawn.  The  iron  is  received 
first  in  a  trough  (Fig.  38)  about  18  feet  long,  22  inches  wide  at 
the  top  and  15  inches  deep,  and  sloping  slightly  from  the  furnace. 
For  a  distance  of  about  12  feet  from  the  furnace  the  trough  is 
permanent,  consisting  of  heavy  castings,  protected  with  sand. 
At  the  lower  end  of  the  trough  is  a  dam,  D,  and  the  skimmer,  S, 
is  placed  a  few  inches  above  this  as  shown.  The  iron,  which  is 
at  first  free  from  slag,  flows  from  the  dam,  and  soon  rises  to  the 
level  of  the  skimmer.  Since  the  slag  floats  on  the  surface  of  the 
iron  it  is  prevented  by  the  skimmer  from  passing  on  with  the  iron. 
Moreover,  sand  is  thrown  above  the  skimmer,  and  pressed  down, 
and  the  skimmer  itself  is  lowered  as  the  level  of  the  iron  falls. 
The  slag  overflows  into  the  trough,  C. 


Fig.  38. 

If  immediate  use  is  to  be  made  of  the  iron  it  is  run  into  brick- 
lined  ladles,1  otherwise  it  is  cast  into  "pigs."  As  a  rule,  the  pigs 
are  molded  in  sand,  the  molds  being  prepared  for  each  cast  with 
the  aid  of  wooden  models.  The  arrangement  of  the  casting  bed 
is  shown  in  Fig.  39.  The  main  channel  through  which  the  iron  is 
led  traverses  the  middle  of  the  bed,  and  tributary  channels  lead 
the  iron  to  the  pig  molds  on  either  side.  The  lowest  set  of  molds 
having  been  filled,  the  iron  is  turned  into  the  other  sets  successive- 
ly by  placing  dams  at  the  points  2,  3,  4,  etc.,  and  cutting  out  the 
side  of  the  main  channel.  After  cooling  the  pigs  with  water  they 
are  broken  from  the  "sows"  by  means  of  sledge  hammers  and 
taken  out.  The  sows  also  are  broken  into  lengths  which  can  be 
handled. 

Pig  machines  are  used  at  many  of  the  large  plants,  thus  dis- 
.  138. 


IRON   SMELTING 


I07 


pcnsing  with  laborers  in  the  casting  shed.  In  the  type  of  machine 
now  in  general  use  the  molds  are  of  steel,  and  are  carried  on  an 
endless  belt  which  is  slowly  revolved  over  sprockets  as  the  iron 
is  poured  in  from  a  ladle.  The  iron  is  cooled  by  water,  and  is 
solid  by  the  time  it  passes  over  the  sprocket  from  which  it  falls 
to  the  ground  or  into  railway  cars. 

Disposal  and  Use  of  the  Slag. — The  cinder-notch,  or  tap-hole 
for  the  slag  is  situated  some  distance  around  the  furnace  from 
and  about  4  feet  higher  than  the  iron-notch.  The  opening  is  through 


Hlllllllllllllllllllll 


39- 


a  water-cooled,  bronze  plate,  and  it  is  closed  by  means  of  an  iron 
plug.  The  slag  is  tapped  as  often  as  is  necessary  to  keep  it  well 
below  the  tuyere  line.  It  is  run  into  iron  ladles,  which  are  mounted 
on  standard-gage  trucks,  and  are  provided  with  the  necessary 
mechanism  for  tilting  them  down  on  side  when  the  slag  is  to  be 
dumped. 

Of  the  enormous  quantity  of  blast  furnace  slag  now  produced 
yearly,  the  larger  part  goes  to  waste.  It  is  being  used,  however, 
for  road  beds,  and  several  railway  companies  have  adopted  it  as 


IO8  METALLURGY 

a  standard  ballast.     A  very  good  quality  of  cement  is  now  manu- 
factured from  slag,  after  extracting  the  sulphur  and  adding  lime. 

Mineral  wool  is  prepared  by  blowing  a  jet  of  steam  through 
molten  slag.  As  the  steam  escapes  it  carries  out  globules  of  slag 
to  which  ar-e  attached  thin  fibers  or  filaments.  The  material  is 
drawn  by  suction  through  an  iron  pipe  which  is  bent  twice  at  right 
angles  and  exhausts  into  a  large  wire  gauze  enclosure.  The  turns 
in  the  pipe 'serve  to  break  off  the  heads  from  the  filaments,  the 
former  passing  through  the  rneshes  of  the  gauze  and  the  latter  be- 
ing detained.  Mineral  w7ool  is  used  as  an  insulating,  non-inflamma- 
ble packing. 

The  slag  is  granulated  for  various  purposes  by  allowing  it  to 
fall  into  water. 

Disposal  of  Flue  Dust. — This  is  a  difficult  problem,  which  has 
not  yet  been  satisfactorily  solved.  Consisting  chiefly  of  iron 
oxide  and'  coke  dust,  it  is  a  good  material  chemically  to  charge 
again  into  the  furnace.  But  it  is  difficult  to  deal  with  on  account 
of  its  being  so  finely  divided.  It  has  been  briquetted  and  used  as 
ore,  but  so  far  the  processes  for  this  treatment  are  too  expensive. 
Now  that  softer  ores  are  smelted  the  amount  of  dust  produced  is 
much  greater. 

Thermal  Requirements  and  Economy  of  Fuel  in  the  Blast  Fur- 
nace Process. — The  chief  improvements  in  blast  furnace  practice 
have  been  in  the  way  of  increasing  the  output  and  lessening  the 
fuel  consumption.  Until  the  year  1880  no  furnace  had  been  built 
to  make  more  than  100  tons  of  iron  in  a  day,  even  with  the  rich- 
est ores,  and  an  average  of  about  3,000  pounds  of  coke  per  ton  of 
iron  was  considered  good  practice.  The  output  has  now  been 
increased  in  many  plants  to  600  tons  per  day,  and  a  number  of 
furnaces  have  made  runs  of  more  than  800  tons  of  iron  in  a  day, 
with  the  ratio  of  1,900  pounds  of  coke  to  the  ton  of  iron  pro- 
duced. These  economies  have  been  attained  by  better  manage- 
ment of  the  hot  blast  with  the  use  of  improved  heating  appar- 
atus; rapid  driving,  which  has  been  made  possible  by  altering 
the  shape  of  the  furnace  and  increasing  the  pressure  and  volume 
of  the  blast,  and  finally  by  drying  the  blast,  the  effect  of  which 
has  been  so  lately  demonstrated  at  Pittsburg. 


IRON   SMKLTING  IOO, 

In  connection  with  the  disbursement  of  heat  in  the  blast  furnace 
it  may  be  interesting  to  note  the  requirements  from  a  purely  theo- 
retical standpoint.  Of  the  total  amount  of  heat  evolved  by  the 
combustion  of  the  fuel,  one  portion  is  absorbed  in  bringing  about 
the  reduction  and  the  fusion  of  the  metal  and  slag ;  a  second  por- 
tion is  lost  to  the  process,  being  represented  by  the  -gas  that  is 
burned  outside  of  the  stoves,  and  a  third  portion  is  lost  altogether 
through  radiation  and  leakage.  The  amount  of  heat  represented 
in  the  first  portion  may  be  calculated  from  the  composition  of  the 
charge,  and  that  in  the  second  portion  may  be  calculated  from  the 
composition  and  volume  of  the  gas.  The  amount  of  heat  wasted 
can  not  be  calculated  at  all  with  any  degree  of  accuracy. 

The  calculations  of  Lothian  Bell  for  the  amount  of  heat  required 
for  smelting  iron  in  the  Cleveland  district,  England,  may  be  stud- 
ied with  profit.1  The  example  below  is  given  to  show  how  the 
heat  units  usefully  applied  may  be  calculated.  The  assumed  con- 
ditions are  that  the  iron  is  reduced  from  dry,  hematite  ore ;  that 
the  ratio  of  iron  to  slag  is  2  to  1.3,  and  that  the  iron  has  the  com- 
position : 

Iron  Manganese  Silicon  Phosphorus  Carbon 

93  2  1-5  O-1  34 

The  heat  units  absorbed  in  smelting  a  ton  of  the  iron  are  found 
as  follows : 

Weight  of  materials  Calories  required  Calories 

and  changes  wrought  per  unit  weight  total 

Iron  reduced 1,860  1,780  3,310,800 

Manganese  reduced  40  2,290  9 1, Goo- 
Silicon  reduced  '....  30  6,414  192,420 
Phosphorus  reduced  2  5,747  u»494 
Carbon  absorbed...  68  8,080  549, 440 

Metal  fused 2,000  28s2  57o,ooo 

Slag  fused 1,300  5°°2  650,000 

5,375,754 

Taking  the  average  consumption  of  carbon  as  1,750  pounds  per 
ton  of  iron  smelted,  the  heat  units  found  in  the  above  calculation 
represent  38  per  cent,  of  the  total  heat  derivable  from  the  fuel. 

1  "  Principles  of  the  Manufacture  of  Iron  and  Steel,"  p.  95. 
1  Gredt's  estimate. 


CHAPTER   XI 


CAST  IRON 

Cast  iron  is,  generally  speaking,  iron  saturated  with  carbon, 
and  containing  other  impurities  in  varying  percentages  according 
to  the  conditions  of  manufacture.  Practically,  it  represents  all 
the  iron  made  in  blast  furnaces,  which  has  not  been  submitted  to  a 
refining  process. 

Properties  and  Uses. — The  main  properties  to  which  cast  iron 
owes  its  wide  applications  are  its  low  fusibility,  and  the  ease  with 
which  it  can  be  molded  into  the  shapes  desired.  In  most  other 
properties  it  is  inferior  to  the  other  forms  of  iron,  the  tenacity, 
elasticity  and  malleability  being  very  low,  and  it  can  not  be  forged 
or  welded.  The  crushing  strength  is,  however,  greatest  of  all 
ordinary  forms  of  metal.  The  cooling  of  fluid  cast  iron  is  at- 
tended, first  by  a  slight  expansion,  but  following  this  there  is  a 
contraction  bringing  the  metal  into  smaller  space  that  was  orig- 
inally occupied. 

In  making  a  casting  a  mold  is  first  prepared,  the  interior  of 
which  bears  the  shape  of  the  casting.  The  molten  iron  is  poured 
in,  and  on  expanding  it  is  forced  into  every  part  of  the  space  and 
reproduces  the  shape.  The  contraction  or  shrinkage  follows,  mak- 
ing the  casting  smaller  than  the  pattern.  Cavities  are  often  form- 
ed in  castings,  and  are  known  as  "pipp"  or  "blow-holes,"  accord- 
ing to  their  origin.  Piping  in  castings  is  due  to  shrinkage.  The 
metal  coming  in  contact  with  the  sides  of  the  mold,  forms  a  solid 
shell,  while  the  interior  of  the  mass  is  still  liquid.  Solidification 
now  proceeds  in  lines  perpendicular  to  the  planes  of  the  surfaces, 
as  shown  in  Fig.  40.  The  outside  being  rigid,  any  contraction 
that  takes  place  will  result  in  the  softer  iron  of  the  interior  being 
drawn  toward  the  outside,  leaving  a  cavity  near  the  middle.  The 
middle  and  upper  portion  of  the  casting  is  the  last  to  solidify,  and 
there  may  be  enough  fluid  metal  above  to  fill  the  cavity,  produc- 
ing a  depression  in  the  top  of  the  castings,  blow-holes  are  caused 


CAST    IRON 


III 


by  dissolved  gases.  The  greater  portion  of  these  gases  passes 
out  of  solution  during  the  cooling.  This  accumulates  in  small 
bubbles,  which  gather  into  larger  ones  as  they  pass  upward 
through  the  molten  metal.  While  the  metal  is  liquid  they  escape, 
but  when  the  crust  forms  the  bubbles  are  arrested,  and  they  now 
accumulate  and  form  cavities  in  the  softest  portions  of  the  viscid 
mass.  The  prevention  of  these  defects  in  castings  will  be  studied 
in  connection  with  steel  casting. 


Fig.  40. 

Grading. — Like  all  other  forms  of  iron  the  properties  of  cast 
iron  depend  principally  upon  its  composition.  It  generally  con- 
tains the  elements,  carbon,,  silicon,  sulphur,  phosphorus  and  man- 
ganese, which  in  their  varying  proportions  to  the  iron,  and  to 
each  other,  afford  the  possibility  of  numerous  varieties  or  grades, 
differing  in  properties..  In  the  manufacture  of  castings  for  var- 
ious purposes  these  different  grades  of  iron  are  used.  A  great 
many  manufacturers  base  their  selection  of  pig  iron  for  castings 
largely  upon  the  appearance  of  the  fracture,  which  is  to  a  certain 
extent,  an  index  to  the  composition  and  properties.  This  relates 
specially  to  carbon  and  silicon. 

The  analyses  and  properties  of  several  commercial  grades  of  pig 
iron  have  been  given  by  J.  M.  Hartman,1  as  follows : 

1  Jour.  Frank.  lust.,  134,  132-144. 


112  METALLURGY 

Grade  12345  6 

Iron 92.37  92.31  94.66  94.48  94-oS  94.68 

Graphitic  Carbon 3.52  2.99  2.50  2.02  2.02 

Combined       "      0.13  0.37  1.52  1.98  1.43  2.83 

Silicon 2.44  2.52  0.72  0.56  0.92  0.41 

Phosphorus 1.25  1.08  0.26  0.19  0.04  0.02 

Sulphur 0.02  0.02  ...  0.08  0.04  0.02 

Manganese 0.28  0.72  0.34  0.67  .   2.02  0.98 

No.  I. — Gray,  with  a  large,  dark,  open-grain  fracture;  softest 
of  all  the  numbers,  and  used  exclusively  in  the  foundry.  Tensile 
strength  and  elastic  limit  very  low. 

No.  2. — Gray,  with  a  mixed  large  and  dark  grain;  tensile 
strength,  elastic  limit  and  hardness  greater  than  No.  i,  and  the 
fracture  smoother.  Used  exclusively  in  the  foundry. 

No.  j. — Gray,  with  a  small  close  grain ;  tenacity,  elasticity  and 
hardness  superior  to  No.  2,  though  more  brittle.  Used  either  in 
the  rolling  mill  or  the  foundry. 

No.  4. — White  background,  dotted  closely  with  small  spots  of 
graphite  (mottled  iron),  and  little  or  no  grain  to  the  fracture. 
Tenacity  and  elasticity  lower  than  No.  3,  but  hardness  and  brit- 
tleness  increased.  Used  exclusively  in  the  rolling  mill. 

No.  5. — White,  with  smooth  grainless  fracture;  tenacity  and 
elasticity  much  lower  than  No.  4,  and  still  harder  and  more  brit- 
tle. Used  exclusively  in  the  rolling  mill. 

The  general  effects  of  the  common  elements  in  cast  iron  may 
be  summed  up  as  follows:  Carbon,  in  the  combined  form,  im- 
parts strength  and  hardness,  excessive  amounts  causing  brittle- 
ness.  It  lowers  the  melting  point  and  produces  a  light,  granular 
fracture.  Silicon  lowers  the  melting  point  and  renders  molten 
cast  iron  more  fluid.  It  acts  as  a  "softener"  in  white  cast  iron, 
in  which  it  causes  the  precipitation  of  graphite.  High  percent- 
ages of  silicon  cause  brittleness  and  weakness.  Silicon  con- 
duces soundness  and  to  a  large  extent  prevents  the  formation  of 
blow-holes  in  castings.  Silicon  irons  have^characteristic,  crystal- 
line fractures.  Sulphur  is  generally  very  objectionable  in  cast 
iron,  since  it  causes  brittleness  and  general  weakness.  As  much 
as  0.25  per  cent,  is  usually  allowable.  Phosphorus  in  large  pro- 
portions develops  extreme  brittleness  and  weakness.  The  shrink- 


CAST    IRON  113 

age  of  cast  iron  during  cooling  is  considerably  lessened,  and  it 
remains  fluid  longer  if  much  phosphorus  is  present.  Greater 
smoothness  may  be  brought  about  on  the  surface  of  castings  by 
the  use  of  phosphorus.  The  range  of  phosphorus  in  ordinary 
cast  iron  is  from  0.5  to  1.5  per  cent.  Manganese,  in  the  normal 
proportions  of  0.2  to  I  per  cent.,  is  beneficial  in  cast  iron,  in- 
creasing its  hardness  and  density  and  suppressing  the  formation 
of  blow-holes.  Excessive  amounts  of  manganese  develop  brittle- 
ness.  It  should  be  borne  in  mind  that  none  of  the  properties  of 
cast  iron  are  affected  entirely  by  a  single  element.  They  may  be 
influenced  by  the  like  or  counter  effects  of  two  or  more  elements. 

IRON  FOUNDING 

No  elaborate  equipment  is  necessary  to  the  manufacture  of 
iron  castings.  A  melting  furnace  and  molds  are  needed,  and 
these  under  shelter,  with  plenty  of  room  for  carrying  on  the 
work.  A  foundry  plant,  however,  may  include  pattern-making 
and  machine  shops  and  other  equipment.  A  brief  description 
of  the  methods  of  melting  and  casting  in  general  use  is  here 
given. 

Melting. — Iron  for  castings  is  most  commonly  melted  in  a 
cupola.  This  is  a  small,  cylindrical  blast  furnace,  built  of  steel 
plates  and  lined  with  fire-brick.  Fig.  41  represents  a  style  of 
cupola  in  general  use.  It  is  provided  with  two  working  doors, 
tap-holes  for  the  iron  and  slag  and  a  double  row  of  tuyeres,  to 
which  the  air  is  supplied  by  way  of  an  annular  blast  box.  The 
walls  are  contracted  at  the  top,  the  shaft  terminating  in  a  stack. 
Sufficient  explanation  of  the  details  are  given  in  the  figure. 

The  cupola  charge  is  made  up  of  alternate  layers  of  iron  and 
fuel  (generally  coke),  with  enough  limestone  added  to  flux  the 
ash.  The  blast  is  cold  and  at  a  pressure  of  but  a  few  ounces. 
It  is  generally  supplied  by  a  fan  or  a  blower  of  the  Root  type. 
A  little  more  than  100  pounds  of  coke  are  required  to  melt  a 
ton  of  iron.  It  is  desirable  to  keep  the  fuel  consumption  as  low 
as  possible,  for  the  sake  of  economy  and  to  prevent,  as  far  as 
possible,  the  further  addition  of  impurities  to  the  iron.  The 
rate  of  melting  depends  upon  the  size  of  the  cupola,  the  blast 
pressure  and  the  composition  of  the  iron. 


METALLURGY 


Tfepnkoltod 


Swinpij  DtmfK  wiik  PW,  fcta. 

DunpwRod. 
Mica  PNP  lob  ia  ItemonMe  PltH. 

blidt  Shtll. 


Section  on  Upper  Tiiyere 


STANDARD  WHITING  CUPOU 


Fig.  41. 


CAST    IRON  H5 

The  iron  tapped  from  the  cupola  will  not  be  the  same  in  com- 
position as  the  charge  of  pig  iron.  A  part  of  the  iron  is  oxidized 
(burnt)  before  fusion  takes  place,  and  this  takes  some  of  the 
silicon  with  it  into  the  slag.  There  is  also  a  loss  of  manganese 
by  oxidation,  and  the  carbon  may  be  largely  changed  from  the 
graphitic  to  the  combined  form.  Sulphur  and  phosphorus  may 
be  partially  removed,  or  more  absorbed  from  the  fuel,  depending 
upon  the  conditions. 

Reverberatory  furnaces  are  used  instead  of  cupolas  in  some 
foundries.  Contamination  from  the  fuel  is  thus  avoided,  and 
the  entire  charges  being  put  in  and  tapped  alternately,  the  iron 
can  be  mixed  as  desired  and  the  composition  controlled.  The 
atmosphere  of  the  furnace  is  made  reducing  by  regulating  the 
supply  of  air  and  directing  the  flame  downward  on  the  metal. 
The  fuel  may  be  either  soft  coal  or  gas.  This  way  of  melting 
iron  is  slow  and  expensive,  the  fuel  consumption  being  very  high. 

Mixing  Iron  in  the  Foundry. — While  it  is  true  that  the  composi- 
tion of  iron  may  vary  considerably  without  apparent  loss  of 
strength,  the  best  castings  are  made  from  iron  that  is  mixed  to  a 
definite  composition,  as  the  tests  go  to  prove.  Foundrymen  are  now 
conducting  an  industry  on  a  scientific  basis,  which  for  many  years 
had  recognized  no  need  for  scientific  aid.  The  heavy  strains  to 
which  castings  are  now  often  subjected  calls  for  the  best  that  can 
be  made  and  these  to  be  the  best  must  ha  ve  the  proper  composition, 
as  well  as  the  proper  shapes  and  thicknesses.  It  is  not  possible 
always  to  draw  the  supply  of  iron  of  the  composition  desired  from 
a  single  source.  Most  foundrymen  keep  several  brands  in  stock 
from  which  to  make  their  mixtures.  Some  require  the  analysis 
with  all  the  iron  they  buy.  With  the  analyses  furnished,  the  mix- 
tures of  the  composition  desired  may  be  calculated,  due  allowance 
being  made  for  the  losses  during  fusion. 

It  not  infrequently  happens  that  the  required  amounts  of  sili- 
con and  manganese  can  not  be  maintained  in  the  charge,  owing 
to  the  loss  of  these  elements  in  the  cupola.  The  deficiency  may 
be  restored  by  adding  these  substances  in  the  form  of  rich  alloys 
after  the  iron  has  been  tapped  (p.  149).  As  is  well  known,  the 
very  ingredients  which  give  desirable  properties  to  a  metal  are 


1 1 6  METALLURGY 

most  injurious  when  present  in  excessive  amounts.  If  in  making 
a  mixture  of  pig  iron,  it  is  found  that  there  is  too  much  impurity, 
this  may  be  corrected  by  melting  relatively  pure  iron  with  it.  Old 
material  such  as  rails,  boilers  and  machinery  are  cut  in  pieces  that 
can  be  handled  and  sold  as  "scrap."  A  quantity  of  such  mate- 
rial may  be  judiciously  used  for  the  above  purpose.  The  use  of 
scrap  is  specially  to  be  recommended  with  iron  high  in  silicon. 

Casting. — Iron  is  most  commonly  molded  in  sand  or  clay. 
Chills  are  molds  made  of  cast  iron,  and  are  used  to  develop  sur- 
face hardness. 

Sand. — The  sand  used  in  a  foundry  is  known  as  "green"  or 
"dry."  By  the  former  term  it  is  meant  that  the  Sand  is  moist 
enough  to  cohere  under  slight  pressure.  In  making  a  green  sand 
mold  a  pattern  in  wood  is  prepared  corresponding  to  the  shape  of 
the  casting.  The  pattern  is  made  larger  than  the  casting  on  account 
of  the  shrinking  of  the  iron.1  The  pattern  is  placed  in  the  proper 
position  and  sand  is  carefully  packed  around  it.  Except  in  case 
the  casting  is  to  be  a  very  large  one,  the  sand  is  held  in  a  portable 
frame  or  box,  made  of  iron  or  wood  and  in  sections  which  can  be 
removed  to  take  out  the  casting.  Air  vents  are  necessary  in  such 
parts  of  the  mold  as  would  be  blocked  from  communication  with 
the  mouth  by  the  inflowing  metal ;  otherwise  the  expansive  force 
of  the  air  would  destroy  the  mold.  For  hollow  castings  a  "core" 
is  needed.  This  is  made  of  sand  and  it  is  supported  by  small  wires 
in  the  proper  position  to  form  the  interior  of  the  casting. 

When  a  great  many  castings  are  to  be  made  from  the  same  pat- 
tern, machines  are  used  for  making  the  molds. 

Dry  sand  molds  are  made  with  sand  containing  enough  clay  to 
make  it  coherent  when  baked.  The  mold  is  shaped  roughly  in  the 
moist  sand,  and  it  is  finished  with  a  tool  after  baking.  No  pat- 
tern is  needed  in  making  dry  sand  molds,  and  they  are  cheaper 
than  wet  sand  if  but  a  single  casting  is  to  be  made.  They  also 
have  the  advantage  of  making  a  smoother  casting,  since  water 
vapor  and  other  gases  are  not  evolved  when  the  hot  iron  comes  in 
contact  with  the  sides. 

1  The  pattern  maker  uses  a  "  shrink  rule,"  which  is  ^  inch  longer  than 
the  ordinary  foot  rule. 


CAST    IRON 


117 


Loam. — This  is  a  clayey  mixture  to  which  carbon  is  often  added. 
It  cements  much  better  than  sand  does  when  baked,  and  it  is  used 
in  molds  whose  walls  must  be  firm  and  not  be  eroded  by  the  run- 
ning metal.  It  is  especially  adaptable  to  the  molding  of  large,  hoi- 


Fig.  42. 

low  castings,  when  the  metal  has  to  travel  some  distance  before 
reaching  every  part  of  the  mold.  They  are  used  exclusively  in  the 


Fig.  43- 

manufacture  of  sewer  pipes.  The  molds  are  made  by  hand  with 
the  aid  of  some  machinery,  and  are  usually  faced  with  a  carbon- 
aceous material.  Since  loam  molds  can  be  used  but  once,  loam 
castings  are  more  expensive  to  manufacture  than  sand  castings. 

Chills. — The  conditions  under  which  gray  iron  is  changed  to 
white  iron  are  recognized  in  the  manufacture  of  chilled  castings. 
A  chilled  casting  is  made  from  gray  iron,  but  the  outer  portion, 


Il8  METALLURGY 

or  a  part  of  it,  is  rapidly  cooled  to  a  certain  depth,  producing 
white  iron  in  that  portion.  This  is  accomplished  by  using  molds 
made  of  cast  iron,  which  cools  the  surface  by  reason  of  its  high 
conducting  power. 

The  section  (Fig.  42)  shows  the  method  of  casting  a  roll  from 
the  bottom,  using  chill  plates  for  the  body  of  the  roll  and  sand 
for  the  ends. 

The  effect  of  the  chill  is  shown  by  the  sketch  (Fig.  43)  in  which 
the  graphite  is  represented  by  the  pen  dashes.  The  depth  of  the 
chill  is  determined  somewhat  by  the  composition  of  the  iron.  A 
deep  chill  is  secured  by  using  a  mold  with  very  thick  walls.  The 
uneven  cooling  of  a  roll  sometimes  causes  internal  stress  sufficient 
to  crack  it. 

Malleable  Castings. — By  a  special  process  of  annealing,  tough- 
ness and  malleability  may  be  developed  to  a  remarkable  degree 
in  white  cast  iron.  In  this  way  castings  are  made  to  answer  for 
lorgings  in  many  cases,  the  casting  being  cheaper  to  make.  The 
castings  must,  in  the  first  place,  be  of  the  proper  grade  of  iron. 
The  carbon  must  be  almost  or  entirely  in  the  combined  form, 
and  it  should  not  fall  below  1.50  per  cent.  The  silicon  should 
be  below  one  per  cent.,  the  sulphur  not  over  0.025,  and  the  phos- 
phorus under  0.25  per  cent. 

The  castings  to  be  annealed  are  first  cleaned  of  any  adhering 
sand,  and  then  carefully  packed  in  iron  boxes  with  hematite,  iron 
scale  or  a  slag  rich  in  oxide  of  iron.  The  material  should  be 
fine  but  not  powdered.  The  boxes  are  made  with  removable  bot- 
toms. The  tops  are  covered  with  an  iron  lid  or  luted  with  mud. 
When  packed  the  boxes  are  placed  in  the  annealing  oven,  which 
is  heated  by  a  direct  flame.  The  temperature  of  the  oven  is  main- 
tained at  about  700°  C.  for  three  days,  or  longer,  depending  upon 
the  size  of  the  castings.  Another  day  is  required  for  cooling  the 
oven,  it  being  essential  that  the  cooling  proceed  slowly. 

The  principal  change  that  takes  place  in  the  annealing  process 
is  the  conversion  of  combined  carbon  into  graphite.  The  graphite 
is  not,  however,  of  the  form  observed  in  gray  cast  iron,  the  flakes 
being  very  small  and  evenly  distributed.  About  20  per  cent,  of 
the  carbon  is  burnt  out  during  the  annealing,  and  some  sulphur 


CAST    IRON  119 

is  eliminated.  The  iron  oxide  used  in  the  annealing  box  is  par- 
tially reduced,  some  being  entirely  spent  in  each  operation.  The 
wasting  away  of  the  box  furnishes  good  packing  material,  which 
is  utilized. 

Testing  Cast  Iron. — With  the  increased  knowledge  of  the  pro- 
perties of  cast  iron  and  the  relation  of  these  properties  to  its 
composition,  and  with  the  higher  duty  that  is  required  of  cast  iron 
in  the  progress  of  manufactures,  naturally  the  methods  of  testing 
it  have  been  improved.  It  is  recognized  and  understood  that  the 
properties  of  cast  iron  are  directly  dependent  upon  its  composition. 
Practically  all  the  pig  iron,  that  is  made  for  foundry  purposes,  is 
graded  by  the  smelter  according  to  analysis,  for  he  expects  to  sell 
his  product  in  this  way. 

But  the  analysis  does  not  reveal  all.  In  many  instances  more 
practical  knowledge  of  the  quality  of  iron  is  gained  from  the  me- 
chanical test  than  could  be  interpreted  from  its  composition.  These 
tests  are  made,  as  far  as  possible,  to  imitate  the  stresses  that  will 
be  put  upon  the  iron  in  actual  service.  The  strains  that  are  ex- 
erted during  the  testing  are  measured  and  recorded.  They  are 
usually  increased  until  the  test-piece  is  broken,  showing  the  ulti- 
mate resistance.  The  test  is  either  made  upon  a  finished  casting, 
which  represents  a  number  of  other  similar  ones,  or  upon  a  spec- 
ially prepared  piece  of  convenient  form.  In  either  case  the  test- 
piece  is  taken  from  the  same  lot  of  iron  as  the  castings  which  it 
represents.  Testing  by  the  first  method  gives  a  direct  value,  while 
the  latter  method  gives  only  the  relative  value. 

The  tests  most  commonly  applied  to  cast  iron  are  two — trans- 
verse and  impact. 

Transverse  Testing. — This  shows  the  resistance  of  the  metal 
to  cross  breaking.  It  represents  a  condition  that  is  most  common 
in  actual  service.  It  is  applied  by  supporting  the  test-bar  at  both 
ends,  and  applying  weights  in  the  middle  until  it  is  broken. 

Impact  Testing. — This  shows  the  resistance  offered  to  shocks 
or  blows.  It  is  applied  both  directly  and  indirectly.  When  the 
material  in  question  is  in  the  shape  of  castings  from  the  same  pat- 
tern, and  such  that  can  be  submitted  to  the  test,  it  is  usually  made 
directly.  Otherwise  a  test-piece  of  convenient  size  and  shape  is 


I2O  METALLURGY 

used.  The  test  is  applied  by  allowing  a  hammer  of  definite  weight 
to  fall  from  a  certain  height,  or  if  supported  like  a  pendulum,  to 
swing  through  a  certain  distance,  and  strike  the  iron.  The  dis- 
tance of  the  fall  is  increased  until  rupture  occurs. 

Note. — The  Pennsylvania  Railroad  requires  the  following  test 
for  car  wheels :  From  each  lot  of  50  wheels  one  is  selected  for 
the  test.  It  is  placed  flange  downward  on  an  anvil  block  weighing 
1,700  pounds.  The  block  is  set  on  rubble  masonry  two  feet  deep. 
It  has  three  supports,  not  more  than  five  inches  wide,  for  the 
wheel  to  rest  upon.  The  wheel  is  struck  centrally,  on  the  hub  by 
a  weight  of  140  pounds,  falling  from  a  height  of  12  feet.  If  the 
wheel  breaks  in  two  or  more  pieces,  after  eight  blows  or  less,  the 
fifty  wheels  represented  by  it  are  rejected.  If  the  wheel  stands 
eight  blows  without  breaking,  the  fifty  are  accepted.  The  test- 
wheel  is  furnished  by  the  manufacturers  with  each  fifty  ordered.1 

In  addition  to  the  above  tests  for  cast  iron,  tests  of  tension  and 
compression  are  sometimes  made.  The  tension  test  is  chiefly  used 
for  iron  made  into  steam  or  air  cylinders.  Compression  tests 
are  rarely  needed,  since  cast  iron  is  not  often  weak  in  this  respect. 
The  hardness  is  sometimes  tested  in  iron  that  is  to  be  machined. 
Turner's  method  of  making  this  test  is  to  determine  the  weight 
that  must  be  brought  to  bear  upon  a  standard  diamond  point  to 
make  it  scratch  upon  the  polished  surface  of  the  iron. 


1  Iron  Age,  48,  292. 


CHAPTER  XII 


WROUGHT    IRON 

Historical. — The  origin  of  wrought  iron  is  not  known.  It  is 
probably  the  form  in  which  the  metal  was  first  prepared,  though 
the  practice  of  hardening  iron  with  carbon  is  also  of  unknown 
origin.  So  far  as  there  is  any  evidence,  the  primitive  method  for 
making  wrought  iron  was  to  reduce  it  with  wood  direct  from  the 
ore  in  small,  rude  furnaces.  The  air  supply  was  furnished  by 
natural  draft,  or  by  means  of  rawhide  bellows  operated  by  hand 
— a  process  still  used  in  Africa  and  India  by  the  savage  tribes. 
Throughout  civilized  Europe,  where  the  iron  industry  was  really 
developed,  various  forms  of  forges  were  instituted,  their  product 
being  malleable  iron.  Most  notable  among  these  was  the  Catalan 
forge,  which  the  illustration  represents  (Fig.  44).  The  term 
hearth  is  also  used  to  designate  this  type  of  furnace.  The  furnace 
was  built  of  brick  in  the  form  of  a  shallow  hearth  with  no  stack. 
A  blast  of  air  was  supplied  through  a  single  tuyere,  by  means  of 
a  water  blower  known  as  the  trompe.  The  water  was  allowed  to 
fall  from  a  reservoir,  through  a  tall  pipe,  into  a  blast  box,  as  shown 
in  the  drawing.  Small  openings  were  made  in  the  pipe  near  the 
top  for  the  admission  of  air.  The  air  was  drawn  in  through  these 
openings  by  the  suction,  and  passing  with  the  water  into  the  box  it 
was  there  slightly  compressed.  The  air  for  the  blast  was  drawn 
from  the  top  of  the  box,  and  the  water  was  allowed  to  flow 
through  an  opening  at  the  bottom.  The  trompe  was  built  almost 
entirely  of  wood.  The  ore  mixed  with  burning  charcoal  was  re- 
duced to  spongy  iron. 

The  American  bloomary  is  a  more  highly  developed  type  of 
forge.  Fig.  45  shows  a  bloomary  half  in  section  and  half  in  ele- 
vation. The  chief  differences  between  this  and  the  older  forges 
are  in  the  tall  stack  above  the  hearth  and  the  arrangement  for 
heating  the  blast.  The  hearth  is  enclosed  partly  by  brick  work 
and  partly  by  water-cooled,  iron  blocks.  The  stack  is  built  of 
brick  and  reenforced  with  iron.  The  blast  is  led  through  pipes 


122 


METALLURGY 


(commonly  three),  which  are  bent  to  fit  in  the  stack  as  shown. 
The  blast  may  acquire  a  temperature  of  400°  C.  or  more.  The 
blast  is  delivered  to  the  hearth  by  a  single  tuyere.  The  iron  ore  is 
reduced  in  contact  with  burning  charcoal,  the  iron  being  removed 


Fig.  44- 

from  the  hearth  in  the  form  of  a  spongy  mass  or  bloom.  It  is 
possible,  however,  by  increasing  the  temperature  to  make  cast  iron 
in  the  bloomary.1 

Furnaces  of  the  above  type  have  also  been  used  in  Germany 
and  other  parts  of  Europe.  They  mark  the  transition  between  the 
forge  and  the  modern  blast  furnace. 

About  the  year  1784,  Henry  Cort  invented  the  indirect  or  pud- 
dling process  for  making  wrought  iron  from  pig  iron. 

1  The  American  bloomary  is  illustrated,  and  the  process  fully  described 
by  T.  Egleston  in  Trans.  Atner.  Inst.  Min.  Eng.,  8,  515 


WROUGHT    IRON 


123 


Properties. — The  better  grades  of  wrought  iron  represent  the 
purest  form  of  commercial  iron.  The  properties,  therefore,  most 
dearly  approach  those  of  pure  iron.  It  is  recognized  by  its  tough- 


Fig.  45- 


ness,  combined  with  softness,  and  especially  by  its  fibrous  fracture. 
The  filaceous  structure  is  developed  during  the  forging  of  the 
iron  by  reason  of  intermingled  slag. 

Wrought  iron  is  the  smith's  favorite,  it  being  the  easiest  to 
forge  and  weld.     It  is  well  adapted  to  the  manufacture  of  thin 


124  METALLURGY 

sheets,  owing  to  its  malleability.     It  is  said  that  wrought  iron  wil! 
riot  stand  vibrations  so  well  as  iron  containing  carbon.1 
MANUFACTURE  OF  WROUGHT  IRON 

As  was  pointed  out  in  the  historical  sketch,  wrought  iron  may 
be  prepared  from  the  ore  by  a  single  operation,  or  from  pig  iron 
by  a  refining  process.  These  are  known  as  the  direct  and  the  in- 
direct processes.  The  latter  process  is  more  commonly  termed 
puddling.  Direct  processes  have  been  practically  abandoned,  and 
no  further  space  will  be  given  to  their  description.  It  is  worthy 
of  mention  in  this  connection,  however,  that  pure  iron  and  steel 
have  been  made  directly  from  the  ore  in  electric  furnaces. 
Whether  or  not  these  experiments  have  any  commercial  value 
remains  to  be  proved. 

The  Puddling  Process. — A  great  deal  of  importance  is  attached 
to  the  process  about  to  be  described,  not  so  much  for  its  direct 
bearing  on  the  metallurgy  of  iron,  but  because  the  principles  in- 
volved are  essentially  those  underlying  all  iron  refining  processes. 
A  study  of  the  simple  experiment,  as  outlined  below,  will  give 
the  student  the  keynote  to  the  theory  of  puddling. 

The  sections  A  and  B  (Fig.  46)  represent  the  muffles  of  a 
small,  gas-fired  furnace.  The  atmosphere  in  these  muffles  is  oxi- 
dizing, and  the  temperature  can  be  raised  above  the  melting  point 
of  pig  iron.  In  muffle  A,  is  placed  a  brick,  and  upon  this  is  placed 
a  piece  of  pig  iron.  In  B  another  piece  of  pig  iron  is  placed  upon 
the  bottom  of  the  muffle,  clay  or  sand  being  packed  around  the 
piece  to  form  a  basin  as  shown.  The  temperature  of  the  muffles 
is  now  raised  and  kept  just  below  the  melting  point  of  the  iron. 
The  surface  of  the  pigs  soon  becomes  coated  with  oxide  of  iron. 
The  silicon  is  also  oxidized,  and  combines  with  the  ferrous  oxide 
forming  a  fusible  slag  (ferrous  silicate).  This  runs  away  leav- 
ing the  surface  of  the  metal  exposed  to  further  action.  The  carbon 
in  the  iron  is  converted  into  carbon  monoxide,  and  then  into  car- 
bon dioxide  which  escapes.  The  manganese  is  oxidized  like  tht 
iron  and  passes  into  the  slag.  Now  it  is  seen  that  if  there  is 
enough  silicon  in  the  pig  to  combine  with  all  the  iron  and  form  a 
fusible  slag  that  will  be  the  ultimate  result  of  the  experiment  in 
1  Trans.  Amer.  Inst.  Min.  Eng.,  26,  1026. 


WROUGHT    IRON  125 

muffle  A.  The  result  in  muffle  B  will  be  different,  since  the  slag 
covers  the  iron  and  protects  it  from  further  oxidation.  If  when 
-enough  slag  has  formed,  the  temperature  is  raised  to  melt  the  iron, 
the  impurities  will  be  removed  by  the  oxidizing  power  of  the  slag. 
The  slag  is  mingled  with  the  metal  so  as  to  bring  the  impurities 
into  contact  with  it.  It  must  obviously  become  richer  in  silica  and 
poorer  in  ferrous  oxide  than  the  slag  in  A.  The  carbon  in  the 
iron  has  a  reducing  action  with  the  ferrous  oxide  in  the  slag.  By 
virtue  of  this,  the  carbon  is  removed  and  the  metallic  content  of 
the  charge  is  increased.  Since  purification  raises  the  melting  point 
of  iron  the  metal  in  B  is  left  in  a  plastic  state. 


Fig.  46. 

The  essential  difference  between  the  above  experiment  and  the 
puddling  process,  is  that  in  puddling  most  of  the  oxide  is  sup- 
plied from  another  source  and  not  derived  from  the  iron. 

Dry  Puddling. — This  name  has  been  given  to  Cort's  original 
process,  because  no  slag  forming  substance  was  added  with  the 
metal  charge.  His  furnace  was  a  small  reverberatory  having  a 
sand  or  silicious  bottom.  As  would  be  expected,  the  hearth  was 
badly  fluxed  with  each  heat.  It  was  considered  necessary  that 
the  iron  be  low  in  silicon.  Such  iron  does  not  become  so  fluid  in 
the  puddling  furnace,  and  much  less  slag  is  formed.  Gray  iron, 
liigh  in  silicon,  was  therefore  subjected  to  a  partial  refining  before 
puddling.  The  description  given  below  of  the  refining  process 
or  "Running  Out  Fire,"  is  taken  from  Percy's  Metallurgy. 

"The  refinery  consists  essentially  of  a  rectangular  hearth,  with 
three  water  tuyeres  on  each  side  inclining  downwards.  The  sides 
and  back  are  formed  of  hollow  iron-castings,  called  'water-blocks,' 
through  which  water  is  kept  flowing,  the  front  of  a  solid  cast  iron 
plate  containing  a  tap-hole,  and  the  bottom  of  sand  resting  on  a 
solid  platform  of  brick  work.  Coke  is  the  fu,el  used  with  cold  blast 
blast  at  a  pressure  of  three  pounds  per  square  inch." 

"The  refinery  being  in  operation,  the  folding  doors  at  the  back 


126  METALLURGY 

are  opened  and  coke  is  thrown  in,  the  charge  of  about  one  ton  01 
one  ton,  two  cwts.  of  pig  iron  is  placed  upon  it  and  heaped  over 
with  coke,  after  which  the  blast  is  let  on.  The  operation  is  facilitat- 
ed by  the  addition  of  30  pounds  of  hammer-slag  or  scale.  The 
metal,  which  melts  in  about  one  and  one-half  hours,  is  then  ex- 
posed to  the  action  of  the  blast,  which  is  strongly  oxidizing,  not- 
withstanding the  superincumbent  layer  of  incandescent  coke.  A 
considerable  quantity  of  cinder  is  formed,  consisting  for  the  most 
part  of  tribasic  silicate  of  protoxide  of  iron.  In  about  two  hours 
after  charging,  tapping  occurs,  the  blowing  usually  lasting  about 
one-half  hour.  The  consumption  of  coke  is  about  four  cwts. 
Cinder  and  the  molten  metal  flow  out  together  along  the  run- 
ning-out-bed in  front,  the  cinder,  of  course,  forming  the  upper- 
most stratum.  This  bed  being  refrigerated,  as  previously  stated, 
the  metal  is  speedily  consolidated.  Water  is  copiously  thrown 
over  the  whole,  while  the  accompanying  cinder  is  still  liquid, 
when  the  latter  puffs  up  into  beautiful  little  volcano-like  craters : 
and  it  is  curious  to  watch  the  molten  cinder  and  water  dancingr 
as  it  were,  together ......  The  water,  which  may  be  conven- 
iently applied  in  a  strong,  jet,  promotes  the  separation  of  the 
cinder  from  the  metal.  The  cinder  is  thrown  aside  to  be  either 
smelted  or  used  for  certain  other  purposes ;  and  the  metal,  usual- 
ly about  three  inches  in  thickness,  is  removed  and  broken  up 
in  pieces  of  the  proper  size  for  puddling.  The  metal  is  white 
cast  iron." 

Pig  Boiling  Process. — This  is  the  modern  puddling  process.  It 
takes  its  name  from  the  fact  that  the  bath  of  metal  and  slag  arer 
very  liquid  at  a  certain  stage,  and  the  escape  of  gases  gives  the 
boiling  effect.  The  chief  difference  between  modern  puddling 
and  the  older  methods  is  in  the  use  of  a  fettling  of  iron  oxide  on 
the  furnace  hearth,  from  which  oxide  is  supplied  to  the  slag  in- 
stead of  its  being  supplied  entirely  by  the  oxidation  of  the  metal. 
Credit  for  this  invention  is  given  to  Joseph  Hall,  who  is  said  to- 
be  the  first  to  use  the  fettling  (1830). 

The  sectional  elevation  of  a  common  type  of  puddling  furnace 
is  shown  in  Fig.  47.  This  is  a  small,  direct-fired  reverberatory 
furnace.  The  grate,  G,  is  rather  large  in  proportion  to  the  size 


WROUGHT    IRON 


127 


of  the  hearth,  H.  The  flame  from  the  fuel  bed  passes  over  the 
fire-bridge,  A,  and  is  deflected  upon  the  hearth  by  the  low  roof. 
The  products  of  combustion  pass  into  the  tall  chimney,  C,  by 
which  a  strong  draft  is  maintained.  The  furnace  is  provided  with 
a  single  working  door  at  the  side,  which  serves  both  for  introduc- 
ing and  withdrawing  the  charge.  Puddling  furnaces  are  some- 
times fired  with  gas  and  oil,  though  the  coal-fired  type  is  the  most 
common. 

The  hearth  of  the  furnace  is  thickly  lined  with  iron  ore,  roll 
scale  or  rich,  ferruginous  slag.     The  fettling,  as  it  is  called,  ex- 


Fig.  47- 

tends  up  the  sides  from  the  hearth,  so  that  it  will  be  well  above 
the  surface  of  the  bath  when  a  charge  has  been  melted.  Before 
charging,  the  melter  examines  the  hearth  of  his  furnace  and  makes 
the  necessary  repairs  to  the  fettling.  This  must  of  necessity  be 
renewed  often  since  it  not  only  acts  as  lining,  but  is  also  the 
flux. 

The  furnace  being  ready  some  slag  from  a  previous  operation 
is  first  charged.  The  charge  of  pig  iron  usually  weighs  about 
four  and  one-half  tons  and  is  charged  cold.  The  process  is  de- 
scribed as  progressing  in  four  stages ;  viz.,  the  melting  down,  the 
quiet  fusion,  the  boiling  and  the  balling  up. 


128  METALLURGY 

1.  The  Melting  Down. — This  begins  soon  after  the  iron  has 
been  charged,  the  temperature  of  the  furnace  being  raised  as  rap- 
idly as  possible.     Fusion  is  further  hastened  by  turning  the  pigs 
over  and  stirring  them  in  the  slag  that  forms. 

2.  Quiet  Fusion. — When  fusion  is  complete  the  bath  is  thor- 
oughly rabbled,  bringing  the  metal  into  more  intimate  contact 
with  the  fettling.     It  is  during  this  stage  that  the  silicon  is  almost 
completely  removed.     No  little  skill  is  needed,  on  the  part  of  the 
melter  in  determining  when  the  silicon  has  been  completely  trans- 
ferred from  the  metal  to  the  slag.     He  learns  to  judge  this  from 
the  appearance  of  the  bath.     The  manganese  is  also  largely  re- 
moved during  this  stage. 

3.  The  Boil. — So  far,  most  of  the  carbon  has  remained  in  the 
iron.     Its  removal  is  hastened  by  first  cooling  the  furnace  until 
the  slag  becomes  more  viscous  and  will  not  separate  so  quickly 
from  the  metal,  and_then  by  stirring  the  bath  thoroughly  to  mix 
the  slag  with  the  metal.     Since  the  slag  is  now  rich  in  iron  oxide, 
this  reacts  rapidly  with  the  carbon,  as  is  evident  from  the  evolution 
of  gases  from  the  surface  of  the  bath.  The  carbon  monoxide  that 
is  formed  takes  fire  with  its  characteristic  pale-blue  flame  the  in- 
stant it  bursts  from  the  surface  of  the  slag.     The  reactions  cause 
a  rise  in  temperature  and  the  slag  becomes  more  liquid.  The  large 
amount  of  gas  escaping  during  the  removal  of  carbon  gives  rise 
to  the  boiling  effect.     There  is  also  a  swelling  of  the  charge,  the 
slag  rising  several  inches  up  the  sides  of  the  furnace,  and  often 
flowing  out  the  door.     A  quantity  of  slag  may  be  drawn  off  at  this 
time,  and  the  difficulty  in  handling  the  metal  at  the  end  of  the 
operation  will  be  lessened  if  the  bulk  of  slag  is  reduced  to  the- 
least  that  is  necessary.     The  boiling  diminishes  with  the  removal 
of  the  carbon,  and  when  the  bath  becomes  quiet  the  operation  is 
finished. 

4.  The  Balling  Up. — The  iron  is  now  in  the  form  of  a  por- 
ous, unfused  mass,  in  which  a  quantity  of  slag  is  still  incorporated.. 
The  melter  breaks  up  the  cake  of  metal  with  a  bar,  and  then 
manipulates  the  pieces  on  the  hearth  of  the  furnace  until  they  be- 
come somewhat  rounded  or  roughfy  shaped  into  balls.  This  is  done 
for  convenience  in  handling,  the  balls  weighing  about  75  pounds- 


WROUGHT    IRON 


129- 


each.  These  balls  of  wrought  iron,  being  now  at  the  temperature 
for  welding,  are  taken  from  the  furnace,  grasped  with  tongs  sus- 
pended from  an  overhead  carrier,  and  placed  under  the  hammer  or 
in  the  squeezer  for  removing  the  slag. 

The  principal  of  the  rotary  squeezer  for  wrought  iron  blooms 
is  shown  in  Fig.  48.  A  heavy  cast  iron  cylinder  revolving  with- 
in an  eccentric  shield  in  the  direction  indicated  by  the  arrow  car- 
ries a  ball  around,  revolving  it  in  the  opposite  direction.  The  cor- 
rugated surfaces  of  the  cylinder  arid  shield  prevent  the  ball  from 
slipping  while  it  is  forced  into  the  diminishing  space. 

The  rolling  of  the  bloom  is  conducted  in  a  manner  similar  to 
the  rolling  of  steel  ingots  (chapter  XVI). 


Fig.  48. 

Modifications  of  the  Puddling  Process. — Although  permitting  of 
many  alterations,  the  practice  of  iron  puddling,  with  the  excep- 
tion of  one  important  advancement,  has  continued  essentially  the 
same  since  its  inception.  The  more  common  practice,  jiist  des- 
cribed, looks  mainly  to  the  removal  of  carbon,  silicon,  manganese 
and  some  phosphorus.  In  some  special  high  grades  of  iron  it  is 
required  that  the  phosphorus  be  practically  eliminated.  This  is  ac- 
complished by  the  use  of  a  basic  slag.  The  slag  may  be  rendered 
basic  by  increasing  the  percentage  of  ferrous  oxide,  or  by  adding 
lime. 

Soda  ash  (impure  carbonate  of  sodium)  has  been  employed  with 
small  quantities  of  iron  for  the  removal  of  phosphorus  and  sul- 
5 


130  METALLURGY 

phur.  While  iron  may  be  desulphurized  with  mixtures  contain- 
ing soda  ash,  this  material  is  far  too  expensive  to  use  on  the  large 
scale. 

A  mixture  of  manganese  dioxide  and  salt  is  sometimes  added 
to  the  charge  at  the  beginning  of  the  heat.  This  renders  the  slag 
more  liquid  and  more  strongly  oxidizing,  favoring  the  removal 
of  phosphorus  and  sulphur. 

Mechanical  Puddling. — Many  attempts  have  been  made  to  con- 
struct a  puddling  furnace  which  can  be  rocked,  tilted  or  revolved 
by  machinery,  thus  bringing  about  the  disturbance  of  the  bath  in- 
stead of  stirring  it  by  hand.  Such  a  furnace  would  be  desirable 
from  more  than  one  point  of  view.  The  labor  of  a  puddler  is 
exceedingly  severe  and  might  well  be  dispensed  with ;  the  process 
might  be  cheapened  by  doing  away  with  such  expensive  labor,  and 
the  output  would  be  increased,  assuming  that  more  material  could 
be  treated  at  the  same  time.  The  mechanical  furnace  has  not, 
however,  proved  entirely  satisfactory,  and  most  of  the  wrought 
iron  is  still  made  by  the  brawn  and  skill  of  the  puddler.  A  me- 
chanical furnace  has  been  designed  and  used  for  some  time  by  J. 
P.  Roe,  of  Pottstown,  Pa.1 


1  Trans.  Atner.  Inst.  Min.  Eng.,  33,  551,  also  Iron  and  Steel  Inst.  Jour., 
1906,  3,  264. 


CHAPTER  XIII 


STEEL— THE   CEMENTATION  AND   CRUCIBLE  PROCESSES 

Definition. — When  steel  was  manufactured  solely  by  the  cemen- 
tation and  crucible  processes,  it  was  understood  as  refined  iron  to 
which  a  definite  amount  of  carbon  had  been  added.  If  it  contained 
less  than  0.5  per  cent,  of  carbon  it  was  known  as  "mild  steel," 
while  the  hardest  steel  contained  1.50  per  cent,  of  carbon.  Since 
the  introduction  of  the  Bessemer  and  open  hearth  processes  for 
making  steel,  the  term  has  had  a  wider  meaning.  By  these  pro- 
cesses iron  practically  saturated  with  carbon,  and  iron  that  is  al- 
most free  from  carbon  may  be  prepared,  but  the  product  is  always 
designated  as  steel.  Furthermore,  there  are  now  on  the  market 
a  number  of  alloys  of  iron  with  other  metals,  all  of  which  are 
known  as  steel,  so  that  the  term  as  now  used  does  not  signify  any 
special  composition.  Since  there  are  now  among  civilized  nations 
four  distinct  processes  in  use  for  its  production,  steel  may  be  de- 
fined as  iron  that  has  been  refined  by  one  of  these  processes — ce- 
mentation, crucible,  Bessemer  and  open  hearth. 

THE  CEMENTATION  PROCESS 

When  iron  and  carbon  are  placed  in  contact  and  heated  to 
about  600°  C.,  they  combine  slowly,  the  carbon  penetrating  the 
iron  to  a  greater  depth  as  the  heating  is  prolonged.  This  phe- 
nomenon is  known  as  cementation.  The  process  of  cementation  is 
one  in  which  the  commercially  pure  iron  is  heated  without  fusion 
in  a  suitably  constructed  furnace,  and  in  contact  with  solid  car- 
bon, until  the  required  amount  of  carbon  has  been  absorbed. 

The  Furnace. — Fig.  49  shows  the  cementation  furnace  in  sec- 
tion. The  rectangular  converting  pots  or  boxes,  in,  which  the! 
iron  is  carburized,  are  built  of  fire-brick  or  stone.  They  are  heat- 
ed by  means  of  flues,  F,  leading  from  the  fire-place,  G,  under- 
neath the  boxes  and  up  their  sides.  The  flues  terminate  in  the 
short  chimneys,  C.  Air  is  excluded  from  the  boxes  by  the  arched 
roof  of  fire-brick,  and  the  entire  furnace  is  enclosed  in  a  conical 


—-••- 
^^*  v^ 

OF  THt          ^X 
;  !  V  i?  D  O  i  T-  vr  a 


132 


METALLURGY 


stack.  The  manhole  and  the  charging  holes,  H,  are  bricked  up 
during  the  operation.  The  test  bars  are  drawn  from  the  boxes 
through  the  small  ports,  T. 


Fig.  49. 

The  Process. — The  steel  is  made  from  selected  bars  of  the  pur- 
est commercial  iron.  Wrought  iron  is  preferred,  though  Bes- 
semer and  open  hearth  steel  are  sometimes  employed.  The  bars 
are  placed  in  layers  in  the  fire-brick  boxes  or  pots,  and  between  the 
layers  charcoal  free  from  dust  is  packed.  Each  set  o-f  bars  is 
placed  at  right  angles  to  those  in  the  layer  below,  and  a  covering 
of  charcoal  is  put  over  the  last  layer  when  the  box  is  full.  The 
boxes  are  made  to  hold  from  10  to  15  tons  of  bars. 

The  boxes  having  been  filled  and  air  excluded  from  the  charge, 
the  fire  is  lighted  and  the  temperature  of  the  furnace  is  slowly 
raised  until  the  maximum  is  reached.  This  requires  about  48 
hours.  The  heating  is  continued  for  from  4  to  10  days,  depend- 
ing upon  the  amount  of  carbon  wanted  in  the  steel.  The  degree 


133 

of  carburization  is  ascertained  from  time  to  time  by  taking  out  a 
bar  through  the  port  provided  and  examining  its  fracture.  When 
the  process  has  proceeded  as  far  as  desired,  the  fire  is  drawn,  or 
allowed  to  die  out,  and  the  furnace  cools  slowly.  Within  five 
days  the  furnace  may  be  entered  and  the  bars,  which  are  now 
carbon  steel,  are  removed.  The  carbon,  however,  has  not  been 
uniformly  distributed  throughout  the  bars.  The  outer  portion 
may  be  saturated,  while  the  center  is  almost  free  from  carbon. 
It  now  remains  to  convert  these  bars  into  steel  of  uniform  com- 
position. They  are  cut  into  convenient  lengths,  and  these  are 
bundled,  heated  to  the  welding  temperature  and  forged  into  a 
single  piece.  The  metal  is  first  coated  with  a  wash  of  clay  and 
borax,  which  checks  oxidation  and  serves  as  a  flux,  giving  a  clean 
surface  for  welding.  Having  been  cut  and  welded  once,  the  steel 
is  known  as  "single  shear."  A  higher  grade  of  steel  is  made  by 
cutting  up  the  bar  and  welding  as  before,  this  being  termed 
"double  shear"  steel.  As  some  carbon  is  burnt  out  during  the  re- 
heating, the  bars  to  be  sheared  are  selected  which  contain  more 
carbon  than  is  required  in  the  finished  product. 

It  is  possible  to  combine  a  little  over  two  per  cent,  of  carbon 
with  iron  by  cementation.  A  further  addition  would  require  a 
higher  temperature,  which  would  result  in  the  fusion  of  the  steel. 
It  is  not  known  whether  the  carbon  diffuses  through  the  iron  as 
carbon,  or  as  a  carbide  of  iron.  It  is  probably  similar  to  the  mi- 
gration of  carbon  in  other  instances,  but  wherein  the  conditions 
are  different,  as  in  chilled  and  malleable  castings.  If  the  steel  has 
been  converted  from  wrought  iron  the  surfaces  of  the  bars,  as 
they  are  drawn  from  the  furnace,  are  covered  with  blisters.  This 
has  given  rise  to  the  term  "blister  steel."  The  cause  of  the  blisters 
has  been  satisfactorily  explained  by  Percy.  The  ferrous  oxide, 
which  is  always  present  in  wrought  iron,  is  reduced  by  the  carbon 
with  the  formation  of  carbon  monoxide,  and  the  gas,  seeking  its 
escape,  distorts  the  plastic  metal.  Cement  steel  that  is  made  from 
iron  containing  no  oxide  or  slag  is  not  blistered. 

The  output  of  cement  steel  is  relatively  very  small.     It  still 
holds  its  own  in  the  manufacture  of  some  tools  and  machinery 


134  METALLURGY 

pieces,  but  the  cheaper  processes  have  obliterated  any  future  for 
it.     The  most  famous  works  are  at  Sheffield,  England. 

THE  CRUCIBLE  PROCESS 

Modern  steel  manufacture  may  be  said  to  have  begun  with  the 
crucible  process.  Although  steel  had  been  converted  in  a  molten 
condition  before  this  time,  it  had  never  been  cast  as  is  done  in  the 
crucible  process,  and  other  important  details  were  lacking.  The 
term  "cast  steel"  was  significant  at  the  time  that  steel  was  made 
either  in  the  cementation  furnace  or  in  the  crucible.  The  crucible 
process  is  the  invention  of  Benjamin  Huntsman,  an  English  manu- 
facturer. His  first  plant  was  erected  at  Sheffield  and  put  into 
operation  about  I74O1  The  process  was  in  every  essential  the 
same  as  it  is  to-day. 

Crucibles. — Steel  melting  crucibles  are  generally  manufactured 
from  a  mixture  of  clay  and  graphite.  Graphite  alone  is  not 
cohesive  enough  to  make  xa  strong  crucible  and  is  expensive, 
while  clay  crucibles  have  too  great  a  tendency  to  shrink  and 
crack  when  in  use.  Clay  crucibles  are  preferable  for  soft  steel 
since  their  walls  do  not  give  up  carbon  to  the  charge.  As  a  rule, 
they  do  not  last  for  more  than  one  melting.  The  graphite  crucibles 
are  much  more  durable.  A  good  crucible  of  American  make  con- 
tains about  50  per  cent,  graphite,  40  per  cent,  clay  and  10  per 
cent.  sand.  Ceylon  graphite  is  considered  the  best  for  crucibles. 
Other  materials  have  been  substituted  for  natural  graphite. 
Kish  and  coke  dust  are  used,  and  old  crucibles  are  regularly 
ground  and  mixed  with  the  new  material. 

The  clay  and  the  graphite  for  the  crucibles  are  ground  and  then 
mixed.  After  making  the  clay  into  a  thin  paste  with  water  the 
graphite  and  sand  are  sifted  in.  The  thickened  mass  is  then 
mixed  in  a  pug  mill  and  allowed  to  stand  for  a  few  days.  By 
allowing  it  to'  stand,  or  tempering  as  it  is  called,  the  clay  loses 
some  water  and  incorporated  gases  and  becomes  stiffen  It  is 
now  ready  to  be  turned  into  crucibles. 

A  lump  of  the  clay  is  kneaded  and  thrown  into  a  plaster  of 
Paris  mold,  corresponding  in  shape  to  the  outside  of  a  crucible. 
The  mold  is  centered  on  a  potter's  wheel,  and  as  it  revolves  a 
1  Jour.  Iron  and  Steel  Inst,  1894,  2,  224. 


STEEL  135 

knife  blade  is  lowered  into  the  clay  to  form  the  interior  of  the 
crucible.  The  knife  is  set  at  the  proper  angle  to  force  the  clay 
upward  and  against  the  walls  of  the  mold.  The  top  of  the 
crucible  is  trimmed,  and  it  is  allowed  to  remain  in  the  mold  for 
about  three  hours.  During  this  time  the  porous  plaster  absorbs 
so  much  water  from  the  clay  that  it  is  left  rigid  enough  to  stand 
up.  The  crucible  is  dried  for  a  week,  and  is  then  ready  for 
firing.  It  is  enclosed  in  a  shell  of  two  clay  seggars  and  placed 
with  other  crucibles  in  a  potter's  kiln.  Both  the  rise  and  fall 
of  temperature  during  the  firing  are  carefully  controlled,  as 
sudden  changes  would  weaken  or  fracture  the  crucibles.  The 
temperature  of  the  kiln  should  be  at  least  as  high  as  that  of  the 
furnace  in  which  the  crucibles  are  to  be  used. 

The  Melting  Furnace. — The  furnaces  used  for  melting  steel 
in  crucibles  are  often  of  very  simple  construction,  consisting  es- 
sentially of  a  melting  hole  in  which  the  crucibles  are  placed,  and 
in  which  coke  is  burned,  and  a  tall  chimney  for  creating  a  draft. 
The  melting  hole  is  covered  with  a  fire-clay  lid  during  the  opera- 
tion. Gas-fired  furnaces,  employing  regenerators  are  also  in 
use. 

The  Process. — Each  crucible  receives  a  charge  of  from  60  to 
90  pounds  of  metal.  The  materials  converted  are  wrought  iron 
or  steel  made  by  one  of  the  cheaper  processes  and  pig  iron.  The 
pig  iron  serves  as  the  carburizer,  or  charcoal  or  anthracite  may 
be  used  instead.  A  little  oxide  of  manganese  is  usually  added, 
and  sometimes  a  "physic"  such  as  salt,  potassium  cyanide,  etc., 
is  used.  The  crucible  is  covered  and  placed  in  the  melting  hole 
of  the  furnace.  Some  time  after  the  charge  has  fused  the 
melter  takes  off  the  crucible  lid  and  examines  the  contents  with 
the  aid  of  a  rod.  From  the  appearance  of  the  slag  and  certain 
other  indications  he  determines  when  the  crucible  should  be  with- 
drawn from  the  furnace.  The  crucible  is  lifted  out  by  means 
of  tongs,  which  are  made  to  encircle  it  a  few  inches  below  its 
largest  diameter,  giving  support  to  its  sides.  The  steel 
is  usually  allowed  to  stand  for  a  few  minutes  before 
pouring.  This  is  termed  "killing,"  as  it  serves  to  quiet 


136  METALLURGY 

the  metal.1  The  steel  is  then  slowly  poured  into  the  ingot  molds, 
and  the  crucible  is  thrown  aside  for  inspection.  A  crucible  lasts 
for  from  four  to  six  heats.  The  molds,  just  referred  to,  are  com- 
monly about  30  inches  long  and  three  inches  square  inside.  They 
are  made  in  two  pieces,  the  joint  running  lengthwise,  and  held 
together  with  rings  and  keys.  This  mechanism  facilitates  the 
removal  of  the  ingot  after  it  has  cooled.  The  large  molds  are 
of  one  piece.  In  case  the  contents  of  one  crucible  is  not  enough 
to  fill  a  mold,  two  or  more  heats  are  poured  at  the  same  time. 
The  ingots  are  reheated  to  the  forging  temperature  and  rolled 
or  hammered  into  the  shapes  desired.  About  10  per  cent,  of 
the  steel  is  rejected  in  the  mill  on  account  of  piping  in  the  in- 
gots. 

It  is  not  possible  in  the  crucible  process  to  determine  the 
amount  of  carbon  that  should  be  added  to  a  charge  to  produce 
the  grade  of  steel  desired,  since  the  losses  are  not  constant.  It 
is  therefore  necessary  to  estimate  the  carbon  in  the  steel  after  it 
is  made  and  to  grade  it  accordingly.  The  fracture  test  is  here 
made  use  of  to  great  advantage.  The  tops  of  the  ingots  are 
broken  off  and  the  fractures  examined  by  a  skilled  inspector. 

The  superior  quality  of  crucible  steel  is  due  to  the  selection 
of  high  grade  materials  to  begin  with  as  well  as  to  the  process 
itself.  With  so  small  an  amount  of  metal,  and  that  in  a  closed 
vessel,  the  composition  of  the  charge  and  the  temperature  of 
working  can  be  almost  completely  controlled.  The  occlusion 
of  gases  is  largely  prevented  by  these  conditions  and  by  the 
manner  of  pouring,  which  is  to  allow  the  metal  to  run  in  a  very 
small  stream. 


1  The  same  result  is  arrived  at  by   adding  silicon  or  aluminum  to  the 
charge  and  pouring  immediately. 


CHAPTER  XIV 


STEEL— THE  BESSEMER  PROCESS 

ACID 

History. — The  Bessemer  process  fittingly  bears  the  name 
of  the  illustrious  inventor,  Henry  Bessemer.  The  process  is  not, 
however,  the  invention  of  a  single  man,  but  of  a  number  whose 
names  should  be  as  closely  linked  with  it  as  that  of  Bessemer. 
The  original  idea  was  not  to  make  steel  directly  by  this  process, 
but  to  make  wrought  iron,  from  which  steel  was  to  be  converted. 
Wm.  Kelly  was  the  first  to  show  that  pig  iron  could  be  purified 
by  blowing  air  through  it  while  in  a  molten  state.  Kelly's  in- 
vention was  what  he  termed  a  "Pneumatic  Process"  for  making1 
malleable  iron.  He  first  carried  out  his  idea  at  Eddyville,  Ky., 
in  1847.  About  ten  years  later  he  built  a  tilting  converter  for 
the  Cambria  Steel  Works,  at  J6hnstown,  Pa.,  where  it  has  been 
preserved.  His  lack  of  financial  backing  prevented  Kelly  from 
making  a  commercial  success  of  the  process  he  had  originated. 
However  much  may  have  been  suggested  to  Bessemer,  no  one 
can  doubt  that  the  unique  construction  of  plant  and  the  details 
of  the  process  were  his  own  achievement.  The  result  of  Besse- 
tner's  experiments  were  first  made  public  in  a  paper  before  the 
British  Association,  in  1856.  He  termed  his  invention  "The 
Manufacture  of  Malleable  Iron  and  Steel  Without  Fuel."  The 
success  of  the  process  was  no  less  a  surprise  to  the  inventor  than 
it  was  to  other  metallurgists,  though  it  had  failed  as  yet  to  con- 
vert iron  into  steel.  The  product  was  simply  iron  from  which 
the  impurities,  except  sulphur  and  phosphorus,  had  been  remov- 
ed, and  this  was  often  red-short  and  difficult  to  work.  After 
some  unsuccessful  efforts  to  remove  phosphorus  Bessemer 
abandoned  the  idea,  since  he  was  able  to  buy  Swedish  pig  iron 
which  was  practically  free  from  phosphorus.  The  other  diffi- 
culties were  overcome  by  adding  spiegel-eisen  to  the  iron  after 
it  had  been  blown,  the  manganese  correcting  the  red-shortness 


138  METALLURGY 

and"  the  carbon  producing  the  necessary  hardness  and  tenacity 
in  the  steel.  This  very  essential  improvement  was  suggested  by 
Mushet.  The  improvements  in  the  building  of  Bessemer  plants, 
and  the  development  of  the  process  are  attributed  largely  to 
Alexander  Holley,  a  famous,  American  engineer. 

The  Iron  Mixer. — At  the  large  iron  and  steel  plants  the  iron 
is  delivered  to  the  steel  works  in  the  molten  condition.  It  is 
run  directly  from  the  blast  furnace  into  brick-lined  ladles,  which 
are  mounted  on  railway  trucks,  and  conveyed  immediately  to  the 
Bessemer  or  open  hearth  shop.1  It  is  obvious  that  a  great  sav- 
ing must  be  realized  by  converting  the  iron  without  further  hand- 
ling or  allowing  it  to  cool.  The  ideal  practice  would  be  to  pour 
all  the  iron  directly  from  these  ladles  into  the  converters,  and 
this  would  be  done  if  the  iron  were  always  of  the  proper  com- 
position, but  this  is  not  the  case.  The  silicon,  in  particular,  is 
too  high  in  some  casts  and  too  low  in  others,  making  it  neces- 
sary to  mix  the  different  grades  of  iron  to  obtain  one  of  the 
proper  composition  for  blowing.  Remelting  cupolas  are  •  gen- 
erally used  in  converting  mills  for  the  sake  of  having  a  reserve 
of  hot  metal.  By  skillful  management  it  is  possible  to  convert 
a  good  deal  of  iron  "direct,"  the  iron  from  the  cupolas  being 
mixed  in  the  converters  with  the  iron  from  the  furnace.  The 
difficulty  is  most  completely  solved,  however,  by  the  use  of  the 
hot  metal  mixer,  an  invention  of  W.  R.  Jones,  of  Braddock,  Pa. 
The  mixer  is  a  large  vessel,  built  of  steel  plates  and  lined  with 
fire-brick.  It  has  a  circular  bottom,  and  is  mounted  on  rollers 
so  that  it  can  be  revolved  to  pour  out  the  contents.  The  iron  is 
run  in  from  a  ladle  through  an  opening  near  the  top  of  the  mixer, 
and  is  poured  out  from  an  opening  on  the  opposite  side.  The 
capacity  of  the  mixer  is  usually  about  300  tons,  which  is  the 
equivalent  of  three  or  four  casts  from  a  large  blast  furnace. 

The  Converter. — The  section  of  a  modern  converter  is  shown 
in  Fig.  50.  The  converter  consists  of  an  outer  shell  of  heavy, 

1  Hot  metal  roads  have  been  built  by  the  Carnegie  Steel  Co.  from  their 
blast  furnaces  at  Braddock  across  the  Monongahela  River  to  their  steel 
plants  at  Homestead  and  Duquesne.  The  molten  iron  is  supplied  to  the 
Bessemer  and  open  hearth  plants  at  a  distance  of  two  miles  from  the  blast 
furnaces. 


STEEL 


139 


cast  steel  plates  and  a  thick  lining  of  ganister  or  other  acid  re- 
fractory material.  It  is  mounted  on  hollow  trunnions,  through 
one  of  which  connection  is  made  for  the  passage  of  the  blast. 
The  converter  is  made  in  three  sections,  any  one  of  which  may 
be  repaired  independently.  The  top  section  is  held  to  the  middle 
section  or  body  of  the  vessel  by  means  of  bolts,  and  the  bot- 
tom section  is  attached  with  hangers  secured  by  keys,  an  ar- 


Fig.  50. 

rangement  which  permits   of   the  bottom  being   renewed   in  a 
very  short  time. 

The  converter  is  lined  with  ganister,  mica-schist  or  other 
silicious  material.  The  stone  is  ground  and  mixed  with  water 
for  use  as  a  mortar.  The  lining  is  made  by  setting  the  cut  stone 
in  the  mortar,  or  by  using  the  mortar  exclusively.  When  the 
latter  method  is  adopted  the  mortar  is  rammed  in  place  after 
placing  a  wooden  core  to  form  the  interior  of  the  vessel.  The 
lining  is  dried  by  a  fire  before  the  vessel  is  put  into  use. 


140 


METALLURGY 


The  bottom  is  the  weakest  part  of  a  converter.  The  lining 
in  the  upper  and  middle  sections  may  need  but  slight  repair  dur- 
ing a  year  of  constant  running ;  while  the  bottom  lasts  but  for 
a  few  heats,  usually  15  to  20.  A  number  of  bottoms  prepared 
for  immediate  use  are  therefore  kept  on  hand  in  converting 
mills.  The  construction  of  the  converter  bottom  warrants  special 
notice.  As  shown  in  the  cut  the  blast  is  received  in  a  cast  iron 
box  through  a  gooseneck,  which  is  connected  with  the  trunnion. 
The  blast  is  let  into  the  charge  through  a  number  of  fire-brick 
tuyeres,  which  are  set  in  openings  in  the  metal  top  of  the  blast 


box  and  surrounded  by  the  lining  material.  The  tuyeres  are 
perforated  by  numerous  holes,  about  half  an  inch  in  diameter, 
through  which  the  blast  is  delivered.  In  this  way  the  blast  is 
distributed  through  the  charge  at  the  moment  it  enters.  De- 
fective tuyeres  are  plugged  by  turning  the  vessel  down,  remov- 
ing the  blast  box  lid  and  tamping  in  clay  from  the  bottom. 

Fig.  51  shows  the  method  of  rotating  a  converter,  the  dot- 
ted outline  indicating  the  position  for  charging.  A  sliding  rack, 
driven  by  a  double-acting,  hydraulic  ram,  meshes  with  a  pinion 
keyed  to  one  of  the  trunnions  on  which  the  converter  rotates.. 


STEEI*  141 

\\"ith  this  device  the  converter  may  be  turned  through  an  angle 
of  180°  or  more.  A  casting  of  iron  prevents  injury  to  the 
mechanism  from  slag  ejected  during  the  blow. 

The  Process. — The  vessel  is  turned  down  to  the  horizontal 
position  and  a  charge  of  8  to  15  tons  of  molten  pig  iron  is 
run  in.  The  blast  is  turned  on  as  the  vessel  is  raised  to  the 
vertical  position.  A  cloud  of  dense,  brown  fume  is  evolved, 
followed  by  a  shower  of  sparks.  A  voluminous  flame  also  ap- 
pears and  vanishes  with  the  cloud.  This  is  followed  by  a  shower 
of  sparks,  and  then  a  short  and  not  very  luminous  flame  appears. 
As  the  temperature  increases  the  flame  grows  in  length  and 
luminosity  until  at  the  end  of  about  eight  minutes  it  reaches 
the  maximum  of  twenty  feet  or  more,  and  is  of  dazzling  white- 
ness. If  the  blow  is  continued  the  flame  soon  declines  rapidly 
until  it  disappears.  At  the  moment  the  flame  drops,  or  before 
that  time,  the  vessel  is  turned  down  and  the  blast  is  shut  off. 
The  ladle  being  in  place,  the  mouth  of  the  vessel  is  brought  down 
until  all  the  metal  and  most  of  the  slag  run  out,  and  when  the 
ladle  is  swung  around  the  vessel  is  completely  inverted  to  empty 
it  of  the  remaining  slag. 

The  blower  is  guided  by  the  appearance  of  the  flame  in  deter- 
mining the  time  at  which  the  blow  should  be  ended.  He  wratches 
it  through  stained  glasses,  and  with  remarkable  precision  he  can 
tell  when  the  carbon  has  been  eliminated  to  the  necessary  degree. 
The  usual  practice  is  to  stop  the  blow  when  the  carbon  has  been 
diminished  to  0.08  per  cent.,  and  if  necessary,  to  carburize  the 
steel  after  it  has  been  poured  into  the  ladle.  The  duration  of  a 
blow  is  from  7  to  14  minutes.  The  purer  the  iron  and  the 
higher  the  pressure  of  the  blast  the  shorter  will  be  the  duration. 

The  manganese  is  added  to  the  steel  as  it  runs  into  the  ladle, 
or  if  much  is  required,  it  is  added  during  the  blow  from  an  over- 
head chute.  In  ordinary  soft  steel  (0.07  to  0.09  carbon)  about 
0.4  per  cent,  of  manganese  is  generally  added,  which  is  suffi- 
cient to  prevent  red-shortness.  If  higher  carbon  steel  is  wanted 
the  carbon  may  be  added  to  the  ladle  in  the  form  of  anthracite 
coal,  or  more  commonly,  the  steel  is  carburized  with  pig  iron, 
if  spiegel-eisen  is  used  carbon  is  introduced  with  it,  since  it 


142 


METALLURGY 


carries  about  4.00  per  cent,  of  carbon.  The  ladle  is  hoisted  by 
the  crane  and  brought  directly  over  the  ingot  molds  into  which 
the  steel  is  poured. 

Fig.  52  represents  a  steel-pouring  ladle  with  a  part  of  the 
wall  cut  away  to  show  the  interior.  The  ladle  is  built  of  heavy, 
steel  plates,  rivetted  together,  and  lined  with  two  courses  of 
fire-brick.  It  is  supported  on  trunnions  projected  from  the  sides 
slightly  above  the  center  of  gravity.  The  hole  through  which 
the  steel  is  poured  is  situated  in  the  bottom  and  near  the  side. 
The  flow  of  steel  is  controlled  by  means  of  a  stopper  which  is 
carried  on  a  sliding  device  attached  to  the  outer  wall  of  the  ladle. 
The  stopper  is  raised  and  lowered  by  aid  of  a  hand  lever.  The 
rod  which  is  suspended  inside  the  ladle  to  carry  the  stopper  is 
protected  from  the  molten  steel  by  a  fire-clay  sleeve  which  is 
made  in  sections.  The  sections  fit  one  into  the  other,  and  the 
joints  are  sealed  with  clay. 


Fig.  52. 

The  slag  from  the  acid  converter  consists  chiefly  of  the  sili- 
cates of  iron  and  manganese,  silica  being  far  in  excess.  The  con- 
verter lining  is  gradually  fluxed  away,  adding  silica  and  alumina 
to  the  slag.  Any  titanium  present  is  oxidized  and  absorbed  by 
the  slag.  Converter  slag  is  often  employed  as  a  silicious  flux 
in  the  blast  furnace.  It  is  difficultly  fusible,  being  viscid  at  the 
temperature  in  the  converter. 

Converter  dust  is  a  mixture  of  slag  and  metallic  oxide  which 


143 

is  ejected  during  the  blow.  It  also  contains  particles  of  iron. 
About  1.25  per  cent,  of  the  weight  of  a  charge  is  thrown  out  with 
each  blow. 

SiO2  FeO  MnO  A12O3  P.O5        Fe  (Metallic) 

Converter  Slag    64.0  15.0  12.0  1.5  0.007  7.00 

"          Dust    23.0  60.0  4.0  0.5  0.045  11-5° 

Theory  of  the  Process. — The  chemical  changes  that  occur  in 
the  Bessemer  converter,  though  proceeding  much  more  rapidly, 
are  probably  almost  identical  with  those  of  the  puddling  process. 
The  air  entering  through  the  multiple  tuyere  openings- is  at  once 
distributed  throughout  the  charge,  accounting  for  the  rapidity 
with  which  the  metalloids  are  removed.  Carbon,  silicon  and 
manganese  are  almost  completely  removed,  phosphorus  and  sul- 
phur remaining  with  the  iron.  If  the  blow  is  continued  until 
the  flame  drops  only  about  0.03  per  cent,  of  carbon  will  be  left. 

The  heat  generated  by  the  oxidation  of  the  metalloids  is  more 
than  sufficient  to  keep  the  steel  in  a  molten  condition.  Most  of 
the  heat  is  derived  from  the  oxidation  of  the  silicon  on -account 
of  its  high  calorific  power,  and  consequently,  high  silicon  irons 
cause  an  overheating  of  the  charge,  leading  to  "wild  heats." 
This  may  be  prevented  by  lowering  the  pressure  of  the  blast 
or  by  diluting  the  charge  with  cold  steel  scrap.  Steam  is  often 
introduced  into  the  blast  for  the  same  purpose. 

BASIC 

Some  of  the  foremost  metallurgists  were  early  led  to  attempt 
the  dephosphorization  of  iron  in  the  converter.  Bessemer  him- 
self worked  toward  this  end,  though  without  success.  The  basic 
process,  by  which  phosphorus  may  be  practically  eliminated,  was 
finally  worked  out  by  Sidney  Thomas  with  the  assistance  of 
Gilchrist,  Martin,  Stead  and  others. 

The  essential  feature  of  all  basic  processes  for  refining  iron 
is  in  the  use  of  a  basic  slag?  the  lining  of  the  furnace  being 
necessarily  of  basic  material.  The  basic  converting  plant  is,  in 
general  construction  and  appointment,  similar  to  the  acid  plant. 
The  converter  is  of  the  same  form,  but  is  lined  with  dolomite  in- 
stead of  a  siliceous  material.  The  dolomite  is  first  thoroughly 
calcined,  then  crushed  and  mixed  with  hot  tar.  The  mixture 


144  METALLURGY 

is  either  rammed  into  place,  a  core  being  used  for  shaping  the 
interior,  or  it  is  pressed  into  bricks  which  are  burnt  at  a  low 
temperature  and  carefully  set. 

The  Process. — The  vessel  is  heated  either  from  a  previous 
•charge,  or  if  new,  by  means  of  a  coke  fire.  Lime,  equal  in  weight 
to  about  15  per  cent,  of  the  weight  of  the  charge,  is  first  thrown 
in,  then  the  metal  is  added  and  the  blow  follows.  To  all  appear- 
ances the  first  part  of  the  blow  is  in  no  way  different  from  the 
*same  period  in  the  acid  process.  It  is  seen,  however,  that  there  is 
-more  "boiling"  and  frothing  of  the  charge  from  the  amount 
•of  slag  ejected.  The  blow  is  continued  a  few  minutes  after  the 
flame  drops,  the  oxidation  of  the  phosphorus  requiring  a  longer 
time  than  that  of  the  silicon  and  carbon.  The  excess  of  lime 
absorbs  the  phosphorus  rapidly,  the  phosphorus  reactions  being 
the  main  source  of  heat  after  the  silicon  is  gone.  With  high 
silicon  irons  it  is  necessary  to  add  more  lime  during  the  "after 
blow"  to  keep  the  slag  sufficiently  basic.  High  silicon  iron  is 
•obviously  not  wanted  for  basic  converters.  As  with  the  acid 
; process  the  mixer  is  almost  indispensable  for  keeping  the  iron 
•of  uniform  composition.  The  iron  should  contain  not  less  than 
2  per  cent,  of  phosphorus. 

But  few  basic  Bessemer  plants  have  been  built  in  America. 
Most  American  irons  are  comparatively  low  in  phosphorus,  and 
most  of  the  high  phosphorus  iron  is  used  in  the  foundry.  Plants 
have  been  erected  at  Troy,  N.  Y.,  and  at  Pottstown,  Pa.  Neither 
£>f  these  are  now  in  operation. 


CHAPTER  XV 


STEEL— THE  OPEN  HEARTH  PROCESS 

This  is  the  latest  process  that  has  been  introduced  for  manu- 
iacturing  steel.  The  work  of  William  Siemens  in  England  and 
of  E.  P.  Martin  in  France  was  the  foundation  upon  which  open 
hearth  practice  has  been  built.  Siemens  was  the  first  to  em- 
ploy a  reverberatbry  furnace  for  melting  and  converting  steel, 
the  high  temperature  necessary  being  easily  attained  after  he 
had  developed  the  regenerative  system  of  firing  with  gas.  The 
principal  feature  in  his  process  was  the  oxidation  of  the  im- 
purifies  in  pig  iron  with  iron  ore,  while  that  of  Martin's  method 
was  in  the  use  of  soft  iron  or  "scrap"  with  the  charge  of  pig 
iron,  and  in  making  the  necessary  additions  of  carbon  and  man- 
ganese at  the  end  of  the  operation.  The  work  of  these  men  was 
contemporary,  having  been  begun  in  the  early  sixties,  and  the 
process  which  they  put  on  so  successful  a  basis  is  rightly  called 
the  Siemens-Martin  process. 

The  rapid  growth  of  this  method  of  steel  making  is  due  to 
the  fact  that  high  grade  steel  can  be  made  from  all  grades  of 
iron,  and  that  the  composition  of  the  product  is  easily  controlled. 
The  open  hearth  process  is  divided,  according  to  the  practice, 
into  the  Acid  and  the  Basic  processes. 

ACID 

All  open  hearth  furnaces  are  of  the  Siemens  type.  The  sec- 
tional drawings  (Figs.  53  and  54)  show  the  principal  parts  of 
an  ordinary  open  hearth  furnace.  The  hearth  is  supported  on 
I-beams  resting  on  girders,  which  in  turn,  are  supported  on  the 
masonry  below.  The  regenerators,  shown  in  Fig.  53,  are  for 
heating  the  air  and  gas  before  they  enter  the  combustion  cham- 
ber of  the  furnace.  They  are  admitted  into  the  regenerators  on 
one  side  while  the  products  of  combustion  are  heating  those  on 
the  opposite  side.  The  products  of  combustion  are  led  first  into 
dust  chambers  (not  shown  in  the  drawings),  which  prevent  the 


146 


METALLURGY 


larger  portion  of  the  dust  and  slag,  carried  over  by  the  draft, 
from  clogging  the  checker-work.     The  products  of  combustion 


Fig.  53- 


are  led  from  the  regenerators  through  horizontal  flues  to  tall 
chimneys.  The  heat  on  the  furnace  hearth  is  intensified  by  the 
arched  roof  which  acts  as  a  reflector. 


Fig.  54- 


Open  hearth  furnaces  are  commonly  built  of  silica  brick  set 
without  mortar,  the  brick  work  being  held  together  by  means 
of  T-rails,  I-beams  and  tie-rods.  Some  of  the  older  furnaces 


STEEL  J47 

are  almost  entirely  enclosed  in  plates  of  iron  rivetted  together. 
The  roof  of  the  furnace  is  the  weakest  part,  lasting  on  an 
average  for  about  275  heats.  The  hearth  of  the  acid  furnace 
is  thickly  lined  with  sand. 

Three  doors  are  provided  for  introducing  the  charge.  The 
doors  are  hollow,  iron  castings,  water  cooled  and  lined  with 
fire-brick.  They  are  raised  by  hydraulic  power.  The  furnaces 
are  charged  by  means  of  electric  machines,  which  operate  on  the 
floor  in  front  of  the  furnaces.  A  number  of  furnaces  are  com- 
monly built  in  line  and  worked  together.  The  materials  to  be 
charged  are  loaded  in  iron  boxes  mounted  on  bogies.  The 
bogies  are  drawn  on  a  track  in  front  of  the  furnaces  so  that  the 
boxes  can  be  handled  by  the  charging  machine.  The  tap-hole  is 
at  the  back  of  the  furnace.  From  this  the  steel  is  conveyed  to 
the  ladle  in  a  detachable,  clay-lined  spout  (Fig.  54).  The  slag 
that  overflows  is  received  in  the  pit  underneath  the  ladle. 

The  Process. — In  early  practice  the  amount  of  metal  refined 
in  the  open  hearth  did  not  exceed  15  tons.  From  30  to  60  tons 
are  now  treated  in  each  operation.  The  charge  may  consist  en- 
tirely of  pig  iron,  or  it  may  be  made  up  largely  of  iron  and  steel 
"scrap."  *  The  pig  iron  is  charged  either  hot  or  cold.  At  some 
plants  it  is  brought  directly  from  the  blast  furnace.  The  use  of 
the  mixer  is  now  becoming  common  in  open  hearth  practice, 
the  advantages  of  which  have  already  been  explained. 

If  the  furnace  is  new  the  gas  is  kept  on  it  for  twenty- four 
hours  before  charging,  so  that  the  hearth  and  chambers  will  be 
thoroughly  heated.  The  furnace  is  then  given  a  light  charge  of 
finishing  slag  from  a  previous  heat,  and  this  is  melted  and 
swashed  over  the  hearth,  and  then  tapped.  The  grains  of  sand 
are  now  cemented  together  and  a  hard  crust  formed  on  the  hearth 
which  will  the  better  withstand  mechanical  abrasion  from  the 
stock.  The  materials  are  loaded  on  the  charging  bogies  and 

1  The  development  of  the  open  hearth  process  has  furnished  a  ready 
market  for  the  waste  product  of  billet  and  finishing  mills,  and  for  old 
material  of  all  kinds.  There  is,  in  fact,  a  steady  demand  for  such  material, 
and  steel  makers  often  stock  quantities  of  scrap  to  draw  upon  in  times  of 
scarcity.  A  great  deal  of  condemned  steel  is  also  worked  up  in  the  open 
hearth. 


148  METALLURGY 

weighed,  and  charged  in  the  following  order:  light  scrap  (tin 
plate,  etc.),  then  the  heavy  scrap,  and  lastly  the  pig  iron.  The 
following  example  may  be  taken  to  represent  a  charge  for  an 
acid  furnace: 


phosphorus  pig  (Hot)  31,000  Ibs. 

"  "  cast  iron  scrap  (Cold)       7,400  " 

Steel  scrap  93,900  " 

The  time  required  for  charging  with  the  improved  machines  is 
about  30-45  minutes.  As  an  average,  about  30  minutes  are  re- 
quired for  preparing  the  furnace  bottom  for  another  heat. 

The  time  required  for  melting  down  the  charge  is  of  course 
considerably  shortened  if  the  pig  iron  is  charged  hot.  Ordinarily 
about  six  hours  would  be  required  for  the  complete  fusion  of 
such  a  charge  as  the  above.  Until  this  stage  is  reached  but 
little  attention  is  needed  on  the  part  of  the  melter,  except  to  re- 
reverse  the  gas  and  air  valves  at  regular  intervals.  A  thin  slag 
forms  at  the  beginning,  and  its  volume  increases  rapidly 
in  proportion  to  that  of  the  metal  during  the  progress  of  the 
heat.  This  slag  consists  of  ferrous  silicate  and  the  silicates  of 
any  other  basic  oxides  present.  The  silicon,  manganese  and 
some  iron  are  thus  transferred  during  the  melting  down  stage, 
and  the  slag  resulting  soon  forms  a  protecting  layer  which  pre- 
vents further  oxidation  of  the  iron.  As  soon  as  the  bath  is  in 
a  liquid  condition  the  melter  throws  in  lumps  of  hematite  ore 
to  hasten  the  decarburization.  The  ore  is  added  at  intervals, 
between  which  tests  are  taken  and  their  fracture  examined,  until 
the  carbon  is  as  low  as  desired.  The  bath  "boils"  soon  after  the 
first  addition  of  ore  on  account  of  the  quantity  of  carbon  dioxide 
evolved.  The  frothing  and  swelling  may  cause  an  overflow  of 
slag  through  the  working  doors.  It  is  during  this  stage  that  the 
greatest  skill  is  needed  on  the  part  of  the  melter.  He  should 
have  the  bath  in  proper  condition  for  tapping  as  soon  as  the 
impurities  are  eliminated.  By  this  is  meant  that  the  slag  should 
be  very  liquid,  so  that  it  will  separate  well  from  the  metal,  and 
as  nearly  neutral  as  possible  at  the  time  of  tapping.  The  tem- 
perature should  not  be  higher  than  is  necessary  to  prevent  vis- 
cosity in  pouring.  In  case  the  slag  has  been  made  strongly 


oxidizing  and  the  carbon  has  been  "worked  down"  below  the 
required  limit  (the  heat  not  being  in  condition  for  tapping)  the 
carbon  may  be  restored  by  adding  pig  iron.  Tests  are  taken 
with  which  to  ascertain  the  composition  of  the  steel. 

When  a  test  is  to  be  taken  the  bath  is  first  stirred  to  establish 
uniformity.  A  long-handled,  soft  iron  spoon  is  then  thrust, 
first  into  the  slag,  and  then  into  the  metal.  The  coating  of 
slag  that  chills  on  the  spoon  prevents  the  metal  from  sticking. 
The  spoon,  holding  about  two  pounds  of  metal,  is  withdrawn 
quickly  and  the  contents  poured  into  a  rectangular,  cast  iron 
mold.  As  soon  as  it  is  solid  the  test  is  knocked  out,  quenched 
under  water  and  broken.  From  the  appearance  of  the  fracture 
the  melters  learn  to  estimate  the  carbon  with  remarkable  accuracy 
when  it  is  as  low  as  0.50  per  cent. 

When  the  heat  is  ready  to  tap,  the  ladle  is  placed  in  the  posi- 
tion shown  in  Fig.  54,  the  spout  being  placed  so  as  to  throw  the 
stream  of  metal  a  little  to  one  side  of  the  center  of  the  ladle. 
This  gives  a  whirling  motion  to  the  steel,  and  facilitates  a 
thorough  and  uniform  distribution  of  the  substances  added.  The 
tap-hole  is  opened  by  two  men  working  from  the  outside  with  a 
hand  drill.  A  signal  is  given  when  a  small  stream  of  metal  ap- 
pears, and  a  heavy  bar  is  thrust  through  from  the  inside  of  the 
furnace.  This  together  with  the  rush  of  the  metal  so  enlarges 
the  opening  that  the  furnace  is  emptied  within  a  few  minutes. 

The  substances  to  be  added  are  thrown  in  with  the  steel  as  it 
runs  into  the  ladle.  Manganese  is  always  added,  since  this  ele- 
ment is  wanted  in  the  steel,  the  initial  manganese  having  been 
transferred  to  the  slag.  Ferro-silicon  and  aluminum  are  also 
used  to  deoxidize  and  to  "quiet''  open  hearth  heats.  "Wild  heats," 
or  those  which  are  highly  charged  with  occluded  gases,  occur  in 
the  open  hearth  as  well  as  in  the  converter.  They  are  said  to 
have  been  held  in  the  furnace  too  long  and  at  too  high  a  tem- 
perature. The  milder  steels  are  always  more  active  while  pour- 
ing. The  common  method  of  adding  carbon  is  to  throw  crush- 
ed anthracite  into  the  ladle.  About  50  per  cent,  of  the  weight 
of  coal  added  is  lost.  Some  specifications  call  for  an  increase 
over  the  initial  phosphorus  and  sulphur.  The  former  is  added" 


150  METALLURGY 

in  the  form  of  a  rich  iron  phosphide  (ferro-phosphorus),  manu- 
factured from  apatite,  and  the  latter  in  the  form  of  stick  sulphur 
or  iron  pyrites.  All  substances  are  added,  so  far  as  possible, 
before  the  slag  comes,  and  they  are  generally  in  the  form  of  small 
lumps.  If  a  large  quantity  of  manganese  is  to  be  added  it  is 
previously  heated  to  insure  complete  absorption. 

As  soon  as  the  furnace  is  empty  the  gas  is  shut  off,  and  the 
hearth  is  prepared  for  the  next  heat.  The  tap-hole  is  closed  by 
placing  a  rabble  over  the  mouth  and  ramming  in  sand  mixed 
with  a  little  clay  from  the  outside.  A  layer  of  sand  is  spread 
over  the  hearth  and  places  that  have  been  worn  or  fluxed  out  are 
patched  with  chrome  ore.  The  further  treatment  of  the  steel 
is  the  same  as  that  of  Bessemer  steel  and  is  described  in  Chapter 
XVI.  For  chemistry  of  the  process  see  next  page. 

BASIC 

The  acid  and  basic  open  hearth  processes  bear  the  same  relation 
to  each  other  as  do  the  acid  and  basic  Bessemer  processes.  The 
general  construction  of  the  basic  furnace  is  identical  with  that  of 
the  acid,  and  the  same  materials  are  put  into  the  walls,  roof  and 
flues.  The  hearth  is  lined  with  calcined  dolomite  which  has  been 
crushed  on  a  disc  with  34-inch  circular  holes.  Magnesite  is 
also  used  in  the  same  way.  Carbon  or  chrome  bricks  are  used 
at  the  juncture  between  the  basic  bottom  and  the  silica  brick 
walls  to  prevent  the  two  substances  from  fluxing. 

Details. — The  following  represents  the  charge  for  a  5O-ton 
furnace : 

High  phosphorus  pig  iron  (Hot)  77,700  pounds 

"       "     (Cold)        8,000       " 

Heavy  steel  scrap  41,900       " 
Light       "       "                        "  200       " 

Limestone  9,000 

Hematite  12,600       " 

The  limestone  and  ore  are  charged  first  so  that  the  hearth  will 
be  protected  from  the  acid  slag  which  forms  at  the  beginning, 
and  so  that  their  chemical  action  will  begin  as  soon  as  the  metal 
fuses  and  trickles  down.  The  limestone  is  generally  charged 


STEEL  IS1 

raw,  the  idea  being  that  the  carbon  dioxide  evolved  from  its 
decomposition  assists  chemical  action  by  agitating  the  bath. 
The  action  of  the  lime  is  not  pronounced  during  the  first  part 
of  the  melting  down  stage,  but  as  the  slag  increases  in  volume 
and  the  temperature  rises  the  lime  reactions  become  more  ap- 
parent. After  the  metal  charge  has  melted  the  melters  say  that 
the  lime  "comes  up/'  and  this  naturally  does  occur,  for  the 
limestone  is  the  lightest  substance  in  the  furnace.  There  is 
much  frothing  of  the  bath  at  this  stage,  due  to  the  decomposi- 
tion of  the  stone  and  to  the  oxidation  of  carbon.  The  steel  would 
be  completely  decarburized  if  left  alone,  but  time  is  saved  as  in 
the  acid  process  by  adding  lumps  of  ore.  The  tests  are  taken 
and  examined  as  before  described.  If  the  steel  is  to  contain 
more  than  0.50  per  cent,  of  carbon  the  Eggertz  test  is  generally 
used.  In  some  instances  chemical  tests  are  made  for  phosphorus 
and  other  ingredients,  to  determine  the  progress  of  the  heat. 

The  fact  that  phosphorus  as  well  as  carbon  is  to  be  worked 
down  generally  means  that  the  basic  process  requires  more  care 
and  watching  than  the  acid  process.  It  is  essential  to  the  com- 
plete elimination  of  phosphorus  that  the  slag  be  basic  and  at 
the  same  time  liquid,  and  since  a  liquid  slag  will  not  stay  mixed 
with  the  heavier  metal,  frequent  stirring  is  required.  Fluor- 
spar is  added  if  the  slag  becomes  too  thick  from  excess  of  lime. 
The  melters  gain  some  idea  of  the  condition  of  the  bath  from 
the  appearance  of  the  slag.  The  bubbles  of  gas  that  escape  dur- 
ing the  period  in  which  the  limestone  is  decomposing  are  small 
and  there  is  much  frothing.  Later  on  the  bubbles  become  larger, 
and  while  the  carbon  is  reacting  with  the  ore  there  is  likely  to  be 
violent  boiling.  The  bath  becomes  tranquil  at  the  time  of  tap- 
ping. 

The  basic  heat  is  tapped  in  the  same  way  as  the  acid,  the  tap- 
hole  being  made  up  and  the  hearth  renewed  with  dolomite  or 
magnesite. 

CHEMISTRY  OF  THE  OPEN  HEARTH  PROCESS 

As  has  been  said  before  the  main  difference  between  acid  and 
basic  processes,  so  far  as  the  result  is  concerned,  is  that  phos- 
phorus is  removed  by  the  basic  treatment.  The  reactions  by 


152  METALLURGY 

which  carbon,  manganese  and  silicon  are  removed  are  alike  in 
both  processes,  and  are  identical  with  those  of  the  puddling  pro- 
cess, except  for  the  differences  that  are  brought  about  by  greater 
mass  and  higher  temperature.  It  is  to  be  borne  in  mind  that  a 
much  larger  quantity  of  metal  is  treated  in  the  open  hearth  than 
in  the  puddling  furnace,  and  that  the  temperature  is  so  high 
that  the  metal  is  kept  in  a  liquid  state  even  after  the  impurities 
have  been  removed. 

Silicon. — This  element  appears  to  be  the  most  readily  oxidized 
of  all  the  impurities.  In  all  refining  processes  it  is  commonly 
said  that  "the  silicon  goes  first."  The  presence  of  basic  ferrous 
oxide  accounts  for  the  removal  of  silicon  during  the  beginning 
or  melting  down  stage  of  the  process.  The  ferrous  oxide  is 
formed  in  two  ways — by  the  oxidizing  flame  sweeping  over  the 
exposed  metal,  and  by  the  partial  reduction  of  the  ore — 

Fe  +  O3  +  Si  =  FeO.SiO,. 
Fe2Os  +  Si02  +  C2  =  Fe  -f  FeO.SiO,  +  2CO. 
By  the  second  reaction  it  is  seen  that  so  long  as  carbon  is  present 
there  is  a  gain  of  metallic  iron  to  the  charge.  Other  bases  such 
as  lime  and  magnesia  would  effect  the  transfer  of  silicon  to  the 
slag,  but  their  action  is  shown  not  to  be  considerable,  from  the 
fact  that  most  of  the  silicon  is  in  the  slag  before  the  lime  reac- 
tions come  into  prominence.  If  the  iron  contains  much  manganese 
this  element  removes  the  silicon  rapidly,  since  its  oxides  are 
strongly  basic  and  readily  formed.  It  is  obvious  that  the  more 
silicon  that  is  present  in  the  charge,  whether  combined  with  the 
metal  or  in  the  ore  and  flux,  the  greater  will  be  the  volume  of 
slag,  if  a  certain  degree  of  basicity  is  to  be  attained.  The  per- 
centage of  silicon  in  the  metal  charge  should  not  exceed  0.75 
per  cent.  Of  course  pig  iron  much  richer  in  silicon  may  be 
used  if  the  heat  be  made  up  largely  of  steel  scrap.  Only  very 
low  silica  ore  and  limestone  are  permissible. 

Carbon. — The  removal  of  carbon  is  effected  chiefly  by  the  ox- 
ides of  iron.  It  is  possible  that  the  carbon  dioxide  from  the 
limestone  plays  some  part,  that  gas  being  reduced  by  carbon. 
The  ore  that  is  added  should  be  in  the  form  of  large  lumps,  since 
fine  stuff  would  float  and  be  absorbed  by  the  slag. 


STEEI,  153 

Phosphorus. — This  element,  like  silicon,  is  acid  forming  and 
has  strong  affinity  for  basic  o>xides.  These  are  neutralized  by 
silica  in  the  acid  process,  and  therefore,  phosphorus  is  not  re- 
moved. Phosphorus  is  more  easily  reduced  than  silicon  and  it 
is  not  so  readily,  eliminated  from  iron  that  is  rich  in  carbon.  The 
addition  of  carbonaceous  material  to  the  bath  in  a  basic  furnace 
will  cause  the  reduction  of  phosphorus,  and  consequently  an  in- 
crease of  the  element  in  the  metal.  Phosphorus  may  be  almost 
completely  removed  in  the  basic  furnace  if  the  bath  is  agitated, 
and  fluor-spar  is  added. 

Manganese. — In  the  acid  furnace  the  manganese  is  practically 
eliminated,  while  under  a  basic  slag  a  considerable  portion  may 
be  retained  in  the  iron.  In  the  basic  process  the  behavior  of 
manganese  appears  somewhat  erratic.  The  separation  from  the 
iron  is  confined,  for  the  most  part,  to  the  melting  down  period. 
Later  tests  not  infrequently  show  an  increase  of  metallic  man- 
ganese in  the  bath.  It  is  probably  reduced  by  carbon  under  the 
influence  of  a  limey  slag. 

Sulphur. — This  element  may  well  be  termed  the  greatest  enemy 
to  the  steel  maker.  There  is  no  reasonably  cheap  method  by 
which  it  can  be  eliminated  to  any  great  extent.  Manganese  has 
been  shown  to  be  the  best  desulphurizer  in  the  open  hearth. 
High  manganese  irons  always  yield  a  product  that  is  proportion- 
ately low  in  sulphur.  It  is  probable  that  in  an  alloy  of  iron 
and  manganese  the  sulphur  combines  with  the  latter  rather  than 
with  the  former,  and  that  the  sulphur  is  oxidized  simultaneously 
with  the  manganese  as  it  passes  into  the  slag.  Some  of  the  sul- 
phur is  undoubtedly  volatilized,  since  an  analysis  of  the  slag  does 
not  account  for  all  that  has  been  eliminated.  A  considerable 
amount  of  sulphur  may  be  removed  by  continued  stirring  in  the 
basic  process,  but  even  under  the  conditions  that  seem  to  be 
most  favorable  the  results  are  uncertain. 

The  figures  below,  taken  from  actual  practice,  show  the  his- 
tory of  an  acid  and  a  basic  heat.  The  composition  of  the 
charges  before  fusion  is  estimated,  the  other  figures  representing 
chemical  analyses. 


154 


METALLURGY 


ACID  HEAT. 


METAI, 


SI.AG 


C  Mn          S               P 

0.80  i.  oo    0.030  0.065 

0.75  0.003  0.026  0.064 

0.76  0.003  0.023  0.074 

0.59  0.003  0.033  0.068 

0.58  0.003  0.027  0.070 


C 
1.50 


Metal 
Mn          S 


SiO2 

(FeOAl203) 

MnO 

CaO 

MgO 

Time 
3:35 

45.ii 

38.98 

15 

15 

0.6o 

O.IO 

10:30 

48.25 

34.70 

16 

4i 

0.48 

0.09 

11:00 
11:15 

51.20 

32.64 

«3 

65 

0.41 

0.09 

11:30 

BASIC  HEAT. 

Slae 

SiO, 

FeO 

A1203 

MnO 

CaO 

MgO 

Time 

5:00 

24.65 

9.00 

9- 

70 

7 

•53 

35-45 

11.70 

12:00 

23-33 

10.40 

9 

86 

8 

.42 

37.13 

10.78 

1:10 

ao.Si 

II.  80 

10 

07 

5 

•  75 

39-38 

11.91 

2:00 

22.38 

11.83 

9- 

95 

7 

58 

39.38 

8.44 

3^5 

i.  oo    0.030    0.075 

1.05  0.21  0.028  0.058 
0.78  0.15  0.028  0.034 
0.48  O.I4  O.O25  O.OI4 

o.io    0.14    0.026    0.013 

The  diagram   (Fig.  55)   shows  graphically  the  rate  at  which 
the  impurities  are  eliminated  in  the  basic  process. 

Relative  Merits  of  Acid  and  Basic  Processes. — The  quality  and 
supply  of  iron  will  determine  the  method  adopted  for  converting  j 
it  into  steel.  It  costs  more  to  convert  steel  in  the  basic  furnace,  I 
basic  refractories  being  more  expensive.  The  acid  process  can 
be  more  easily  controlled,  and  there  is  more  certainty  as  to  the 
composition  of  the  steel.  The  acid  furnaces  would  undoubtedly 
predominate  if  the  larger  part  of  the  iron  supply  was  low  in 
phosphorus.  But  such  is  not  the  condition  in  the  United  States. 
Most  of  the  low  phosphorus  iron  is  treated  in  Bessemer  con- 
verters, and  the  supply  of  Bessemer  ores  is  rapidly  being  ex- 
hausted, unless  new  important  discoveries  are  to  be  made. 
High  phosphorus  iron  is  cheaper  and  more  abundant,  and  there 
is  an  ever  increasing  supply  of  scrap  which  is  unsuitable  for  the 
acid  treatment.  Thus  the  higher  cost  of  the  basic  process  is 
offset.  As  to  the  quality  of  the  steel  it  may  be  said  that  while 
the  stock  is  superior  to  begin  with  and  the  product  more  even  in 
the  acid  process,  just  as  good,  and  even  better  steel  may  be  made 
by  the  basic  process.  The  danger  of  overheating  while  the  heat 
is  prolonged  for  the  removal  of  phosphorus  may  be  guarded 
against  by  proper  management.  The  basic  furnaces  now  greatly 
outnumber  the  acid.  Judging  from  its  phenomenal  growth  and 


STEEL 


155 


present  conditions,  the  basic  open  hearth  process  seems  destined 
to  take  first  rank  in  the  output  of  steel  in  America. 


RECENT  ADVANCES  IN  OPEN  HEARTH  PRACTICE 
Tilting  Furnaces. — The  improvements  in  the  open  hearth  pro- 
cess have  been  chiefly  mechanical.     The  exceedingly  laborious 


156 


METALLURGY 


-and  expensive  method  of  charging-  by  hand  has  been  superseded 
by  machine  charging,  and  the  electric  crane  has  been  instituted 
for  hoisting  and  moving  materials  about  the  plant.  With  the 
75-ton  ladle  crane,  the  heat  of  steel  is  poured  and  removed  from 
the  shop  within  15  minutes  from  the  time  of  tapping.  One  of 
the  most  important  inventions  is  the  tilting  furnace,  which  has 
paved  the  way  to  some  remarkable  improvements  in  recent  prac- 
tice. The  Campbell  furnace  is  mounted  on  rollers  as  shown  in 
Fig.  56.  The  furnace  is  tilted  for  charging  and  pouring  by 


Fig.  56. 

means  of  a  hydraulic  ram.  Aside  from  the  mechanical  feature 
the  furnace  is  similar  in  construction  to  the  stationary  hearth. 
The  Wellman  furnace  is  constructed  and  operated  in  somewhat 
the  same  manner  as  the  Campbell  furnace,  except  that  it  is 
mounted  on  rockers  instead  of  rollers,  and  when  tilted  the  whole 
furnace  moves  forward,  instead  of  rotating  about  its  own  axis. 
The  Talbot  Process. — This  process,  the  invention  of  Benjamin 
Talbot,  has  been  in  successful  operation  for  several  years.  It  is 
otherwise  known  as  the  "Continuous"  process.  A  tilting  furnace 
of  the  Campbell  or  Wellman  type  is  employed  and  the  process 


STEEL  :57 

is  conducted  as  follows :  The  charge  consists  entirely  of  molten 
pig  iron  and  limestone,  and  the  heat  is  worked  down  in  the  usual 
way  with  the  necessary  additions  of  ore  and  stone.  When 
iinished  the  bulk  of  the  slag  is  poured  off  and  a  part  of  the  metal 
is  taken.  The  larger  portion  of  the  metal  is  left  in  the  furnace 
to  which  pig  iron  is  immediately  added  until  the  weight  of  the 
metallic  charge  is  restored.  A  new  slag  is  formed  with  the 
further  addition  of  limestone  and  iron  oxide,  and  the  purifica- 
tion of  the  bath  is  continued  as  before.  The  large  amount  of 
refined  iron  that  is  left  in  the  furnace  after  each  pouring  takes 
the  place  of  the  steel  scrap  used  in  ordinary  practice,  while  it 
protects  the  furnace  hearth  from  the  corrosive  action  of  slags. 
The  time  required  for  tapping  is  saved,  and  there  is  a  further 
gain  of  time  in  the  charging  and  from  the  fact  that  no  cold  metal 
is  used. 

Talbot  furnaces  have  been  installed  at  the  Jones  &  Laughlin 
Works,  Pittsburg,  with  satisfactory  results.  The  capacity  of 
one  of  these  furnaces  is  200  tons  per  day,  or  nearly  double  that 
of  the  stationary  furnace. 

The  Bertrand-Thiel  Process. — This  process  as  applied  to  the 
basic  treatment  employs  two  furnaces,  the  iron  being  charged 
into  one  furnace  and  transferred  to  the  other  after  partial  con- 
version. The  primary  furnace,  or  the  one  receiving  the  charge, 
is  generally  built  on  a  higher  level  than  the  secondary  furnace, 
so  that  the  metal  can  be  transferred  by  gravity. 

The  molten  pig  iron,  limestone  and  ore  are  charged  into  the 
primary  furnace,  and  treated  in  the  usual  way  until  the  silicon 
and  phosphorus  are  removed.  The  charge  is  then  tapped  into 
the  secondary  furnace,  and  the  decarburization  is  finished  under 
a  new  slag.  The  slag  of  the  first  operation  is  separated  from 
the  metal  as  far  as  possible  before  it  is  transferred.  The  de- 
carbonization  is  completed  in  a  much  shorter  time  with  the  foul 
slag  thus  disposed  of,  and  further  purification  as  regards  other 
elements  is  more  easily  accomplished. 


CHAPTER  XVI 


FURTHER  TREATMENT  OF  IRON  AND  STEEL 

The  mechanical  and  heat  treatment  of  steel  are  the  subjects 
dealt  with  in  this  chapter.  In  this  connection  special  reference 
is  made  to  Bessemer  and  open  hearth  steel,  since  these  represent 
so  large  a  proportion  of  the  total  steel  produced.  The  history 
of  the  steel  is  given,  as  it  passes  through  the  several  mills  which 
prepare  it  for  the  market. 

Casting  the  Ingots. — The  quality  of  steel  depends  very  largely 
upon  the  conditions  under  which  it  is  cast.  The  so  called  "wild 
heats"  are  those  which  have  been  held  in  the  furnace  too  long 
and  poured  at  too  high  a  temperature.  A  large  quantity  of  gas 
is  absorbed  by  the  overheated  steel,  causing  the  motion  in  the 
ladle  and  molds,  and  resulting  in  red-shortness,  blowholes  and 
general  unsoundness.  Very  pure  steel  is  specially  liable  to  in- 
jury under  such  conditions.  These  defects  may  be  largely  dimin- 
ished by  pouring  at  the  lowest  temperature  possible,  and  allowing 
the  metal  to  run  in  a  very  small  stream.  It  is  not  practicable, 
however,  to  resort  to  such  measures  with  the  quantities  of  steel 
to  be  handled  from  converters  and  open  hearth  furnaces,  and 
special  methods  for  treating  ingot  metal  have  been  resorted  to. 
The  use  of  manganese,  silicon  and  aluminum  as  deoxidizers  has 
already  been  mentioned.  Blowholes  and  red-shortness  may  be 
almost  completely  eliminated  by  adding  one  of  these  substances : 
while  the  steel  is  being  poured. 

The  closing  of  cavities  in  steel  ingots  by  compression  has  been 
practiced  for  some  time,  though  the  cost  of  installing  and  operat- 
ing compression  machinery  precludes  its  general  use.  The  pres- 
sure is  applied  while  the  ingot  is  cooling  from  the  liquid  state, 
and  is  exerted  upon  the  ends  or  the  sides.  Lateral  pressure  would 
appear  to  be  preferable  for  closing  pipes  and  preserving  the 
structure  of  ingots.  The  value  of  liquid  compression  has  not 
been  fully  demonstrated.  Cavities  are  closed  and  the  steel  is 
made  more  compact,  but  weakness  may  remain  from  failure  of 


FURTHER    TREATMENT    OF    IRON    AND    STEEL, 


159 


the  cavity  walls  to  unite,  as  for  example,  if  the  surfaces  are 
coated  with  oxide. 

Instead  of  casting  from  the  top,  as  is  usually  done,  sounder 
ingots  may  be  made  by  casting  from  the  bottom,  the  tops  of  the 
molds  being  closed.  This  method  of  casting  has  only  been  used 
for  small  ingots,  except  in  rare  instances.  Mention  is  also  made 
of  the  method  of  preventing  piping  by  keeping  the  upper  part  of 
the  ingot  hot  during  the  cooling  of  the  mam  portion,  so  that  the 
pipe  will  be  filled  with  molten  metal. 

Stripping  the  Ingots. — The  train  of  bogies,  each  bearing,  two 
ingots  in  their  molds  is  brought  from  the  Bessemer  or  open 


Front  Elevation  of 
mold 


Fig.  57- 

hearth  shop  directly  to  the  stripper.  Fig.  57  represents  a  bogie 
with  the  ingots  in  position  as  they  were  cast.  The  bogie  has  a 
fiat  top  and  upon  this  rests  the  stool,  or  receptacle  for  the 
mold.  One  of  the  molds  with  the  stool  and  ingot  is  shown  in 
section.  The  stools  are  heavy  slabs  of  cast  iron  with  guards  at 
the  corners  to  hold  the  molds  in  position.  The  molds  are  also 
of  cast  iron,  and  are  made  in  different  sizes  to  hold  from  2  to  4 
tons  and  more  of  steel.  They  are  tapered  slightly  toward  the 
top  and  open  at  both  ends,  the  bottom  being  closed  when  the 
mold  is  placed  upright  on  the  stool.  Lugs  are  cast  at  the  top 
of  the  mold  for  use  in  lifting  it. 


160  METALLURGY 

The  usual  style  of  stripper  is  an  overhead  crane,  spanning  two 
tracks,  and  provided  with  a  travelling  hoist.  From  the  hoist  are 
suspended  two  pairs  of  loops  properly  spaced  for  engaging  the 
lugs  of  both  molds  as  they  stand  on  the  bogie.  The  hoist  is  also 
provided  with  two  rams,  operated  by  water,  and  capable  of 
striking  heavy  blows  upon  the  heads  of  the  ingots  while  they 
are  suspended  a  short  distance  above  the  bogie.  The  crane  and 
hoist  are  propelled  by  means  of  motors  so  that  the  stripping  can 
be  carried  on  with  great  rapidity.  The  loaded  bogies  are  brought 
in  on  the  one  track,  and  the  molds  are  lifted  until  they  are  clear 
of  the  tops  of  the  ingots,  and  then  placed  on  empty  bogies  on 
the  other  track.  Any  ingots  that  stick  may  be  knocked  out  by 
means  of  the  rams. 

The  Soaking  Pits. — If  the  ingots  were  allowed  to  stand  in  the 
air  they  would  at  no  time  during  the  cooling  be  in  the  proper 
condition  for  forging.  When  the  interior  has  become  solid  the 
outer  portion  will  have  become  too  cold.  If  the  initial  heat  were 
evenly  distributed  the  ingot  could  be  forged  without  applying  any 
external  heat.  It  was  in  recognition  of  this  fact  that  the  first 
"soaking  pits"  were  designed.  They  were  simply  brick-lined 
cells,  built  underground  and  adjacent,  each  cell  or  pit  being 
large  enough  to  hold  one  ingot.  The  cover  for  the  pits,  also 
lined  with  fire-brick,  was  mounted  on  wheels  to  facilitate  open- 
ing and  closing.  On  being  placed  in  the  pits,  immediately  after 
stripping,  the  rapid  cooling  of  the  ingot  was  arrested,  heat  being 
reflected  upon  its  surface  from  the  walls  of  the  pit,  and  the  heat 
trom  the  interior  was  given  time  to  soak  out.  This  kind  of  pit 
has  gone  out  of  general  use,  since  it  was  found  difficult  to  have 
the  ingots  in  the  proper  condition  at  the  time  they  were  needed 
in  the  mill,  and  of  course  it  was  impossible  to  heat  cold  ingots 
to  the  rolling  temperature. 

The  soaking  pits  as  now  used  are  arranged  to  be  heated  in- 
dependently with  coal  or  gas.  Cold  ingots  may  therefore  be 
charged  and  brought  to  the  rolling  temperature  and  those  direct- 
ly from  the  stripper  are  quickly  tempered.  The  pits  are  usually 
large  enough  to  hold  four  ingots.  The  train  of  ingots  is  brought 
in  from  the  stripper,  and  the  ingots  are  placed  in  the  pits  by  an 


FURTHER  TREATMENT  OF  IRON  AND  STEEL  161 

overhead,  travelling  crane.  The  ingot  is  seized  near  the  top  by 
tongs  which  are  suspended  from  the  hoist.  The  same  crane  is 
used  for  drawing  the  ingots  from  the  pits  when  they  are  to  be 
rolled. . 

Forging. — Steel  is  forged  by  rolling,  hammering  and  pressing. 
The  rolling  process  is  the  most  used,  being  most  economical  and 
rapid.  The  other  processes  serve  special  purposes  and  will  be 
described  later.  The  ingot  is  rolled  down  to  different  sizes  and 
shapes,  depending  upon  the  requirements  of  the  finishing  mills. 
If  it  is  reduced  to  sizes  less  than  6  inches  square  and  sheared,  the 
pieces  are  called  billets;  if  larger  than  that  the  pieces  are  blooms, 
and  if  rolled  flat  they  are  slabs.  There  are  a  number  of  types 
of  rolling  mills,  each  type  being  designed  for  special  work. 
Mills  take  their  names  from  their  general  construction,  size  of 
the  rolls,  manner  of  working  and  nature  of  the  product.  Brief 
descriptions  of  a  few  important  types  of  mills  are  given  below. 

The  Blooming  or  Slabbing  Mill. — This  mill  is  designed  for  re- 
ducing ingots  to  blooms  o,r  slabs.  It  may  also  be  run  as  a  billet 
mill.  It  commonly  consists  of  two  large  rolls,  driven  by  a  re- 
versing engine,  and  a  series  of  "live  rollers"  for  moving  the 
steel.  The  succession  of  rollers  extends  from  both  sides  of  the 
mill  rolls  in  a  horizontal  plane.  The  rollers  are  revolved  col- 
lectively, to  move  the  steel  in  either  direction,  by  means  of  a 
small,  reversing  engine.  The  mill  rolls  are  of  cast  steel,  which 
is  superior  in  strength  to  chilled,  cast  iron,  of  which  most  rolls 
are  made.  The  bearings  or  chocks  for  the  rolls  are  supported  in 
heavy,  cast  iron  housings.  The  upper  roll,  with  its  chocks,  is 
adjustable  to  the  thickness  of  the  piece  of  steel. 

In  reducing  the  size  of  the  piece  the  pressure  must  be  applied 
in  two  directions,  so  that  the  thickness  both  ways  will  be  as  de- 
sired, and  the  sides  true.  This  is  accomplished  by  turning  the 
piece  over  between  passes,  or  by  employing,  in  addition  to  the 
usual,  horizontal  rolls,  a  pair  of  vertical  rolls  to  act  upon  the 
piece  at  the  same  time.  In  the  former  type  of  mill,  mechanically 
operated  tilters  are  employed  for  turning  the  work  over.  The 
latter  type,  employing  two  sets  of  rolls,  is  known  as  the  universal 

mill 
6 


102 


METALLURGY 


The  phoi  >graphic  view  of  a  universal,  slabbing  mill  is  shown 
in  Fig.  58.  The  power  for  this  mill  is  furnished  by  separate, 
reversing  engines,  the  horizontal  rolls  being  driven  by  the  larger 
engine,  the  base  of  which  is  on  the  floor  level.  The  vertical 
rolls,  which  are  driven  from  the  top  by  the  smaller  engine,  are 
not  visible  in  the  cut.  The  live  rollers,  together  with  the  small 
engine  and  gear  for  driving  them,  are  shown. 

By  a  closer  examination  of  the  cut  the  connection  between  the 
engine  and  the  horizontal  rolls  may  be  traced.  The  driving 
shaft  of  the  engine  carries  a  pinion  which  meshes  into  the 
pinion  of  a  short,  horizontal  shaft  in  line  with  the  lower  roll. 
The  pinions  are  split,  and  the  two  parts  set  so  that  the  teeth  are 
staggered.  This  gives;  a  steadier  motion  to  the  gearing  and 
diminishes  shock  to  the  teeth.  The  shaft,  above  mentioned,  is 
coupled  with  the  lower  of  two  pinions,  which  are  enclosed  in  the 


Section  through 
Wobbler 


Section  through 
Coupling 


59- 


housings  shown  between  the  engine  and  the  roll  housings.  The 
pinions  are  coupled  with  the  rolls  by  spindles  with  wobblers  at 
both  ends.  The  mechanism  of  these  couplings  will  be  under- 
stood from  the  cross-sections  shown  in  Fig.  59.  The  ends  of 
the  spindles  and  of  the  roll  necks  are  cast  in  the  form  shown  in 
the  section  to  the  left.  Three-lobed  wobblers  are  also  in  use, 
but  this  is  the  most  common  form.  The  coupling  box,  shown 
also  in  cross-section,  is  a  heavy,  steel  casting  which  fits  loosely 
over  the  wobblers  of  the  two  members  in  line.  In  the  union 


Fig.  58 -Slabbing  Mill  at  Bethlehem  Steel  Works.     (Mesta  Machine  Co.) 


FURTHER  TREATMENT  OF  IRON  AND  STEEL 


163. 


thus  made  there  is  considerable  play  when  the  mill  is  reversed.. 
The  ends  of  the  spindle  wihich  drives  the  upper  roll  are  tapered 
so  that  they  can  work  freely  in  the  coupling  boxes  when  the 
roll  is  raised  or  lowered.  The  bearing  for  this  spindle  is  sup- 
ported on  beams  which  are  hung  from  the  pinion  housing  and 
the  chock  of  the  upper  roll,  so  that  it  follows  the  spindle  to  any 
angle. 

The  upper  roll  is  raised  and  lowered  by  means  of  two  large 
screws  driven  by  a  motor,  and  a  similar  mechanism  is  employed 
for  adjusting  one  of  the  vertical  rolls.  Indicators  are  provided 
for  showing  the  distance  between  the  rolls. 

The  Three-High  Mill. — This  mill  employs  three  horizontal  rolls 


Fig.  60. 

in  vertical  line  as  shown  in  Fig.  60,  which  represents  the  ar- 
rangement of  rolls  in  a  rail  mill.  The  end  elevation  to  the  right 
shows  the  directions  in  which  the  rolls  turn.  The  mill  is  not 
reversed,  but  the  piece,  after  passing  between  the  middle  and 
bottom  rolls,  is  passed  in  the  opposite  direction  between  the 
middle  and  top  rolls.  The  rolls  are  so  cut  as  to  give  the  pro- 
per openings  for  diminishing  the  cross-section  and  imparting 
the  proper  shape  to  the  piece.  This  obviates  the  necessity  of 
adjusting  the  rolls  after  each  pass.  Different  sets  of  rolls  are 
substituted  for  shapes  that  can  not  be  rolled  by  the  set  in  the 
stand. 

The  three-high  mill  was  invented  by  John  Fritz,  and  first 
operated  in  1857,  at  the  Cambria  Steel  Works,  Johnstown.  It 
was  offered  as  an  improvement  over  the  aid-fashioned  "pull- 


164  METALLURGY 

over"  mill,  which  had  two  rolls,  and  not  being  reversible,  neces- 
sitated the  return  of  the  metal  idle  after  each  pass. 

The  Continuous  Mill. — A  very  large  percentage  of  the  costs  to 
manufacturers  arises  from  the  handling  of  material.  The  numerous 
shapes  now  in  demand  require  as  many  different  kinds  of  rolls, 
and  in  most  instances  the  metal  must  be  carried  from  the  bloom- 
ing or  billet  mill  to  the  finishing  mills.  Here  the  piece  must  be 
reheated  to  the  rolling  temperature,  adding  another  serious  ex- 
pense. The  ideal  in  rolling  mill  practice  is  continuous  rolling 
under  the  initial  heat,  not  allowing  the  metal  to  stop  in  its 
course  until  finished.  Continuous  mills  are  now  in  use  for  manu- 
facturing billets,  rods,  rails,  angle-bar^  and  other  standard 
shapes.  They  consist  of  a  series  of  rolls,  working  in  pairs,  and 
all  driven  by  a  single  engine.  Since  the  metal  must  travel  faster 
in  front  of  each  pair  of  rolls,  on  account  of  the  reduction  in  size, 
each  pair  of  rolls  must  turn  faster  than  the  preceding  pair  to 
prevent  the  piece  from  buckling.  "Flying  shears,"  an  ingenious 
device  for  cutting  the  metal  while  in  motion,  in  pieces  of  any 
length,  may  be  used  if  sawing  can  be  dispensed  with.  Aside 
from  the  savings  above  noted,  and  a  saving  in  labor,  the  "crop 
ends"  are  less  when  continuous  rolling  is  practised.  The  con- 
tinuous mill  can  be  made  to  pay  only  when  there  is  a  steady  de-' 
mand  for  the  shapes  which  it  is  possible  for  it  to  make.  The 
cost  of  installation  is  high,  though  the  output  is  correspondingly 
high. 

Hammer  Forging. — The  steam  hammer  has  supplanted  the 
older  forms.  As  seen  from  the  illustration  (Fig.  61)  it  consists 
of  a  steam .  cylinder  mounted  upon  massive  columns,  the  piston 
rod  carrying  the  hammer,  and  the  anvil  in  position  to  receive 
the  impact.  The  structure  is  seated  upon  a  rubble  and  concrete, 
foundation.  The  hammerman,  in  operating  the  steam  valve,  has 
such  complete  control  of  the  machine  that  he  can  cause  the  ham- 
mer to  exert  a  pressure  of  a  few  pounds  upon  the  work  or  to 
strike  a  blow  of  many  tons.  The  rapidity  of  the  blows  can  also 
be  regulated  as  desired. 

Press  Forging. — The  forging  of  metal  by  continuous  pressure 
differs  from  rolling  in  that  the  pressure  is  exerted  on  the  entire 


Fig.  61— Double-stand,  Steam  Hammer.     (Alliance  Machine  Co.) 


FURTHER    TREATMENT    OF    IRON    AND    STEEL  165 

piece  at  once.  It  differs  from  hammering  in  the  same  respect 
and  in  that  there  is  no  sudden  impact.  The  press  is  now  used 
for  heavy  forging,  especially  in  the  manufacture  of  armor  plates. 
Hydraulic  presses  are  the  most  satisfactory,  the  pressure  cylin- 
ders being  made  from  solid  steel  castings.  A  pressure  of  several 
tons  per  square  inch  is  exerted. 

Of  the  three  methods  of  forging  iron  and  steel,  rolling  is  by 
far  the  cheapest  and  most  rapid.  Hammered  forgings  are 
superior  to  rolled,  being  more  compact  and  less  liable  to  crys- 
talline structure.  There  are  many  shapes  which  can  not  be 
formed  between  rolls,  and  for  forgings  of  irregular  shapes  the 
hammer  is  indispensable.  Still  more  compactness  and  uniformity 
of  structure  is  gained  in  press  forging.  The  large,  unwieldy 
pieces  are  more  easily  handled  in  the  press,  since  the  position  of 
the  piece  does  not  have  to  be  changed  as  with  the  hammer. 

In  all  forging  operations  the  force  of  the  pressure  or  impact 
should  be  sufficient  to  take  affect  with  the  particles  of  the  in- 
terior of  the  piece  as  well  as  those  of  the  exterior.  If  insuffi- 
cient force  is  used,  as  by  employing  too  light  a  hammer,  the  ef- 
fect will  be  shown  at  the  edge  of  the  piece.  This  will  appear 
concave,  indicating  that  the  interior  of  the  piece  has  not  been 
extended  as  much  as  the  exterior.  The  failure  of  forgings  has 
often  been  ascribed  to  this  unequal  working  of  the  metal. 

Reheating. — Iron  or  steel  to  be  forged  should  be  carefully 
heated,  and  shielded  as  far  as  possible  from  the  air.  At  the  high 
temperature  to  which  it  must  be  heated,  the  metal  itself  becomes 
"burnt"  and  red-short  by  exposure  to  air,  and  in  the  case  of  steel, 
some  carbon  is  lost  by  oxidation.  To  avoid  burning  the  furnace 
is  heated  with  a  reducing  flame.  The  proper  temperature  for 
forging  has  not  been  determined  with  exactness.  It  varies 
with  different  grades  of  steel,  being  lower  for  the  high  carbon 
steels.  The  application  of  pyrometry  to  the  heat  treatment  of 
steel  will  doubtless  aid  metal  workers  in  securing  and  controlling 
the  proper  temperatures  in  the  heating  furnaces. 

The  modern  reheating  furnace  is  fired  with  gas,  and  is  of  the 
reverberatory  type.  Billets  are  heated  in  a  long,  narrow  chamber 
through  which  the  flame  passes.  They  are  introduced  at  the 


1 66  METALLURGY 

flue  end  and  advanced  in  succession  toward  the  fire  end  from 
which  they  are  discharged,  the  operation  being  continuous.  By 
this  method  of  heating  the  billets  are  raised  gradually  to  the 
forging  temperature,  and  all  are  exposed  to  the  same  conditions. 

Tempering. — The  word  temper  as  applied  to  steel  denotes  de- 
gree of  hardness.  It  is  unfortunately  used  in  two  senses.  With 
the  steel  maker  it  often  refers  to  different  steels  containing  vary- 
ing amounts  of  carbon,  the  hardening  element,  while  the  steel 
worker  uses  the  same  term  in  referring  to  the  hardness  of  the 
same  steel  under  different  treatment,  affecting  the  hardness.  Car- 
bon has  the  property,  more  than  any  other  element,  of  imparting 
different  degrees  of  hardness,  tenacity,  etc.,  under  different  con- 
ditions of  heat  treatment.  Tempering,  as  here  dealt  with,  re- 
fers to  the  heat  treatment  of  carbon  iron.  It  is  a  subject  that 
has  directed  the  attention  of  men  from  very  remote  times,  and  it 
is  still  an  important  one  for  experiment  and  research. 

The  hardness  of  steel  containing  less  than  0.25  per  cent,  of 
carbon  is  not  greatly  altered  under  different  conditions  of  cool- 
ing. The  effect  of  heat  treatment  is  most  marked  in  steels  con- 
taining from  0.80  to  1.25  per  cent,  of  carbon.  Such  steels,  though 
relatively  very  hard,  still  retain  some  toughness  and  malleability, 
when  cooled  from  a  bright,  cherry-red  heat.  If  cooled  sudden- 
ly they  become  exceedingly  hard  and  brittle,  the  hardest  steels 
often  cracking  from  internal  stresses.  The  properties  of  steel 
are  therefore  affected  by  {he  rate  of  cooling.  A  slow  cooling  or 
toughening  process  is  known  as  annealing,  and  a  rapid  cooling 
or  hardening  process  is  quenching.  Steel  to  be  annealed  may 
be  kept  in  the  furnace  in  which  it  was  heated,  the  temperature 
being  slowly  diminished,  cooled  in  the  air,  or  surrounded  and 
cooled  in  lime,  charcoal  or  other  material  of  low  heat  conduc- 
tivity. In  quenching  the  heated  steel  is  commonly  placed  un- 
der water  or  oil. 

When  a  piece  of  steel  is  heated  it  begins  to  redden  at  about 
400° C.  As  the  temperature  is  raised,  bright  redness  develops,  a 
further  rise  giving  a  dark-yellow.  Higher  temperatures  develop 
a  bright-yellow,  approaching  whiteness.  At  some  point,  varying 
under  different  conditions,  the  temperature  of  the  steel  sudden- 


FURTHER    TREATMENT    OF    IRON    AND    STEEL  167 

ly  rises,  as  is  indicated  by  a  brightening  of  the  color.  The  same 
phenomenon  occurs  during  the  cooling  from  higher  tempera- 
tures, though  not  at  the  same  temperature.  It  is  due  to  some 
change  which  the  carbon  and  iron  undergo,  not  fully  under- 
stood, and  is  termed  recalescence.  When  heated  to  the  recales- 
cence  point  the  metal  is  in  the  plastic  state,  and  at  the  best  tem- 
perature for  forging,  annealing  and  quenching.  At  a  tem- 
perature above  the  heat  of  recalescence  the  steel  loses 
plasticity  and  passes  into  the  granular  state,  malleability  being 
much  impaired,  and  lastly  it  melts.  The  heat  of  recalescence, 
or  the  best  temperature  for  annealing,  etc.,  is  about  665°  C. 
This  varies  slightly  with  steels  containing  different  percentages 
of  carbon. 

One  other  point  is  to  be  considered  in  adjusting  the  temper 
of  steel.  Due  regard  has  not  only  to  be  paid  to  the  amount  of 
carbon  in  the  steel  and  to  the  rate  of  cooling,  but  also  to  the 
temperature  at  which  the  piece  is  cooled.  The  range  of  tem- 
peratures from  which  steel  is  quenched  for  the  hardness  desired 
is  between  220°  and  320°  C,  the  lowest  temperature  yielding  the 
hardest  steel.  The  common  practice  is  to  heat  the  hardened 
steel  somewhat  above  the  maximum  temperature  and  to  quench 
at  the  proper  stage  of  cooling.  If  the  surface  of  the  piece  be 
brightened  the  changes  of  temperature  will  be  indicated  by  the 
changes  of  color  due  to  films  of  oxide.  Though  not  always 
so  convenient,  better  results  may  be  obtained  by  raising  the  steel 
to  the  proper  temperature  instead  of  to  a  higher  temperature 
and  cooling  down.  In  careful  work  the  pieces  to  be  tempered 
are  heated  in  a  bath  of  oil  or  lead,  the  temperature  of  which  is 
regulated  by  aid  of  a  thermometer.  In  the  table  below  are 
given  the  approximate  temperatures  and  their  characteristic 
colors,  above  mentioned. 


c° 

221 
232 
243 
254 
265 

277 
288 

293 
316 

F° 
430 

45° 
470 

49° 
510 
530 
550 
560 
600 

Color 
Very  pale  yellow 
Pale  Straw 
Full  yellow 
Brown 
Brown,  dappled  with  purple  spots 
Purple 
Bright  blue 
Full  blue 
Dark  blue 

Articles 
Lancets 
Surgical  razors 
Common  razors,  pen-knives 
Small  scissors,  cold  chisels,hoes 
Axes,  planes,  pocket  knives 
Table  knives,  large  shears 
Swords,  watch  springs 
Fine  saws,  augers 
Hand  and  pit  saws          —Percy- 

1 68  METALLURGY 

The  Development  of  Surface  Hardness— Case  Hardening.— By 
the  process  known  as  case  hardening  the  surface  only  of  a  piece 
of  iron  is  hardened  with  carbon  while  the  interior  is  soft  and 
tough.  The  piece  is  finished  in  soft  steel,  which  is  then  packed 
with  nitrogenous,  organic  material  in  an  iron  box  and  heated 
for  some  time  at  redness.  The  materials  commonly  used  are 
clippings  of  hoof,  leather,  bone  and  other  animal  matter.  On 
heating,  a  destructive  distillation  takes  place,  and  the  carbon 
enters  the  iron  by  cementation.  As  the  workman  removes  the 
piece  from  the  box  he  drops  it  immediately  into  a  quenching 
liquid,  being  careful  to  shield  it  from  the  air  to  prevent  oxida- 
tion. By  skillful  manipulation,  however,  a  beautiful  mottled 
appearance  may  be  secured  from  short,  unequal  exposure.  Some 
parts  of  light  machinery,  and  of  firearms,  which  should  be 
tough,  and  at  the  same  time  hard  on  the  surface,  are  case  hard- 
ened. 

A  process,  similar  to  case  hardening  in  principle,  is  in  use 
on  the  large  scale  for  improving  armor  plates.  In  this  country 
it  is  known  from  the  name  of  its  inventor  as  the  Harvey  pro- 
cess, or  as  "Harveyizing."  Two  plates  are  placed  one  upon  the 
other  in  a  reheating  furnace,  a  layer  of  charcoal  being  packed 
between  so  that  it  comes  in  contact  with  the  surfaces  to  be 
hardened.  These  surfaces  are  quenched  with  water  after  the 
plates  have  been  taken  from  the  furnace.  Krupp's  method  is 
.similar  to  this,  except  that  hydrocarbon  gases  are  led  between 
the  plates,  the  gases  depositing  carbon  at  the  temperature  re- 
quired for  cementation. 

Specifications. — The  "International  Association  for  Testing 
Materials"  has  for  its  aim  the  perfection  of  methods  for  testing 
steel  and  the  determination  of  the  requirements  that  should  be 
made  of  the  different  grades  of  steel  for  all  important  work. 
The  American  and  foreign  specifications  differ  somewhat, 
though  the  effort  is  being  made  to  have  standards  adopted 
which  will  be  accepted  in  all  countries.  Specifications  are  in- 
tended to  cover  the  modes  of  manufacture,  physical  properties, 
composition,  finishing,  testing,  branding  and  inspecting  the 
steel.  The  requirements  of  course  differ  with  steel  intended  for 


FURTHER    TREATMENT    OF    IRON    AND    STEEL 


169 


different   purposes.     The  American   standard   specifications   for 
steel  rails  are  here  given.1 

CHEMICAL  COMPOSITION. 


Weights  per  yard 

Carbon  # 

Manganese  # 

Silicon  %        Phosphorus  % 

50-59    Ibs 

0-35-0.45 

0.70-1.00 

O.2O                     O.IO 

60-69      " 

0.38-0.48 

0.70-1.00 

O.2O                     O. 

10 

70-79      " 

0.45-0.55 

0.75-1.05 

O.2O                     O. 

10 

80-89      " 

0.48-0.58 

0.8o-l.IO 

O.2O                      O. 

IO 

9O-IOO   " 

0.50-0.60 

0.8o-I.IO 

O.2O                      O. 

10 

DROP  TEST. 

Weights  per  yard 

Height  of  Drop 

Foot-pounds 

45-55 

Ibs 

14  feet 

28,000 

55-65 

<  < 

15    " 

30,000 

65-75 

« 

16    " 

32,000 

75-85 

<  < 

17    " 

34,000 

85-100 

" 

18    " 

36,000 

The  steel  for  rails  may  be  either  Bessemer  or  open  hearth. 
If  it  is  Bessemer  steel  a  test-piece  is  taken  from  every  fifth  heat. 
The  test-piece  is  four  to  six  feet  long,  and  it  is  cut  from  the  rail 
while  hot.  The  piece  is  supported  at  the  ends  with  the  head 
upwards  while  the  drop  test  is  being  applied. 


1  A.  L.    Colby's  paper — "Comparison  of   American   and  Foreign  Rail 
Specifications."     Jour.  Iron  and  Steel  Inst.,   1906,  3,  189. 


CHAPTER  XVII 


COPPER— ORES,  PROPERTIES,  ETC. 

Historical. — Copper  was  the  best  known  and  the  most  abun- 
dant of  the  metals  before  the  age  of  iron.  Records  show  that 
it  was  manufactured  and  used  in  the  remotest  times.  Numer- 
ous specimens  of  copper  utensils  and  ornaments  have  been  pre- 
served, many  of  which  are  known  to  be  thousands  of  years  old. 
Ancient  tools  were  made  of  copper,  it  being  hardened  by  the 
presence  of  some  impurity,  probably  oxygen.  It  was  also  employ- 
ed by  the  ancients  in  alloys  of  brass  and  bronze.  Perhaps  the 
chief  use  of  copper  was  in  this  capacity  until  electricity  became 
known. 

ORES 

Native  Copper  occurs  in  many  localities  in  small  quantities,, 
usually  associated  with  other  copper  ores.  The  famous  Lake 
Superior  deposit,  which  is  worked  chiefly  in  Michigan,  is  the 
only  one  of  metallurgical  significance.  It  was  the  chief  source 
of  copper  in  this  country  until  the  Western  mines  became  so 
productive.  The  Lake  ore  is  disseminated  through  silicious 
rock  from  which  it  is  separated  by  stamping.  Often  large  masses 
of  tough  metal  are  encountered,  making  the  mining  difficult. 

Chalcopyrite  (Cu^S,  Fe,S3)  is  a  widely  distributed  and  very 
important  ore  of  copper.  It  commonly  occurs  in  silicious  and 
other  crystalline  rocks,  and  is  rarely  ever  pure.  The  ratio  of 
the  iron  to  the  copper  is  quite  variable.  Lead,  zinc,  nickel  and 
the  precious  metals  are  sometimes  associated  with  chalcopyrite. 
The  copper  deposits  of  the  New  England  and  Middle  Atlantic 
states  consists  largely  of  chalcopyrite  as  do  those  of  the  Rocky 
and  Sierra  Nevada  Mountains. 

Chalcocite  (Cu2S)  otherwise  known  as  copper  glance  is  an  ex- 
ceedingly rich  ore  when  pure,  though  it  is  usually  mixed  with 
other  sulphides.  It  is  commonly  met  with  in  the  Montana 
mines,  and  it  is  now  regarded  as  the  most  abundant  ore  of  cop- 


COPPER  171 

per.     Chalcocite  is  the  original  ore  from  which  the  others  are 
derived. 

Tetrahedrite,  (Cu2S,  FeS,  ZnS,  AgS,  PbS)4  (Sb2S3,  As2S3) 
is  rarely  ever  a  valuable  ore  of  copper,  though  it  often  contains 
enough  silver  to  pay  for  its  treatment.  It  is  sometimes  an  ob- 
jectionable ingredient  of  other  ores  on  account  of  the  arsenic, 
antimony,  etc.  it  contains.  The  more  valuable  occurrences  of 
this  ore  are  in  Colorado. 

Malachite,  (CuCO3,  CuOH2)  is  relatively  an  unimportant  ore, 
though  a  very  valuable  one  when  sufficiently  pure.  It  is  com- 
mon in  Arizona  and  New  Mexico. 

Cuprite  and  Melaconite,  the  oxides  of  copper  occur  as  pro- 
ducts of  the  natural  decomposition  of  sulphide  ores,  though  in 
but  small  quantities.  The  most  remarkable  occurrences  are  in 
Virginia,  North  Carolina  and  Tennessee.  The  leading  copper- 
producing  states  are  Montana,  Arizona,  Michigan  and  Utah. 
It  is  mined  in  almost  every  state  of  the  West,  and  in  many  of 
the  Eastern  and  Southern  states,  notably,  Tennessee  and  Vir- 
ginia. 

PROPERTIES 

Pure  Copper. — With  but  one  exception,  copper  is  the  only 
metal  with  a  distinct  color.  The  fractured  surface  is  pinkish- 
red,  and  a  somewhat  lighter  color  is  developed  when  the  sur- 
face is  polished.  The  specific  gravity  is  8.945,  according  to 
Hampe.  Owing  to  the  porosity  of  commercial  copper  the 
specific  gravity  varies  from  8.2  to  8.5.  Copper  ranks  among 
the  softer  metals;  it  is  exceedingly  tough  and  tenacious,  highly 
malleable  and  ductile.  These  properties  may  be  illustrated  in 
this  way — a  vessel  of  the  shape  desired  and  with  very  thin  walls 
may  be  hammered  from  a  solid  block  of  the  cold  metal — a  bar 
of  iron  plated  with  copper  and  drawn  into  a  fine  wire,  is  still 
coated  with  the  red  metal.  The  melting  point  of  copper  is 
given  by  Violle  as  about  1,054°  C.  When  molten  it  appears  a 
sea-green,  mobile  liquid.  Just  before  reaching  the  fusion 
point  copper  is  so  brittle  that  it  may  be  powdered.  While  in 
the  liquid  state  it  will  absorb  most  gases  except  carbon  dioxide.1 

1  Hampe    states  that  with  hydrocarbon  gases   only  the  hydrogen  is 
absorbed,  the  carbon  being  liberated. 


172  METALLURGY 

Upon  solidification  the  gases  are  released.  For  this  reason 
sound  copper  castings  can  not  be  made  unless  the  operation 
be  carried  on  in  an  atmosphere  of  carbon  dioxide,  or  unless  some 
substance  is  added  to  hold  the  gas  in  solution. 

One  of  the  most  useful  properties  of  copper  is  its  electric  con- 
ductivity, which  is  excelled  only  by  that  of  silver.  Copper  dif- 
fuses readily  with  most  of  the  common  metals.  Its  alloys  are 
numerous  and  widely  used. 

Effect  of  Impurities. — The  properties  of  copper  are  greatly 
altered  by  the  presence  of  foreign  elements,  some  rendering  it 
quite  unfit  for  certain  purposes  even  when  present  in  minute 
quantities.  Of  the  more  important  impurities  that  have  to  be 
dealt  with  are  bismuth,  arsenic,  antimony,  silicon,  sulphur,  phos- 
phorus and  oxygen. 

Bismuth  has  been  termed  the  copper  maker's  worst  enemy, 
on  account  of  its  deleterious  effects  and  the  difficulty  of  eliminat- 
ing it.  The  presence  of  but  0.05  per  cent,  of  this  element  ren- 
ders the  metal  both  red-short  and  cold-short.  Extreme  brittle- 
ness  is  developed  in  copper  containing  more  than  o.io  per  cent. 
of  bismuth. 

Arsenic  is  the  most  objectionable  impurity  in  conductivity 
copper.  This  property  is  greatly  diminished  if  but  a  few 
hundredths  of  a  per  cent,  of  arsenic  be  present.  The  metal  may 
be  readily  worked,  however,  if  as  much  as  0.50  per  cent,  be  pres- 
ent. A  small  amount  of  arsenic  is  said  to  increase  the  tensile 
strength  of  copper. 

Antimony  has  a  similar  effect  to  that  of  arsenic.  Its  effect 
seems  to  be  less  pronounced  with  very  small  proportions,  while 
with  quantities  exceeding  0.50  per  cent,  the  effect  is  more  marked 
than  that  of  an  equal  amount  of  arsenic. 

Silicon  lowers  the  conductivity  of  copper  when  as  much  as 
0.50  per  cent,  is  present.  Three  per  cent,  does  not  seriously 
impair  the  toughness  and  malleability.  Larger  proportions  pro- 
duce brittleness.  Silicon  is  always  to  be  found  in  unrefined 
copper. 

Sulphur  is   usually   present   in   unrefined   copper.     It    lowers 


COPPER  173 

the  malleability,  as  much  as  0.50  per  cent.,  causing  cold-short- 
ness. 

Phosphorus  is  not  often  present  in  sufficient  quantity  to  in- 
jure the  properties  of  copper.  Red-shortness  develops  with  as 
much  as  0.50  per  cent,  of  phosphorus. 

Oxygen  is  always  present.  In  small  quantities  it  may  be  dis- 
regarded entirely.  With  increasing  amounts  above  one  per 
cent,  the  copper  becomes  harder  and  finally  unworkable. 

Compounds  and  Reactions  Especially  Useful  in  the  Study  of 
the  Metallurgy  of  Copper. — Oxides. — Two  oxides  of  copper  are 
known — cuprous  oxide  (Cu.,0)  and  cupric  oxide  (CuO).  Both 
of  these  compounds  are  formed  when  copper  is  heated  in  oxygen, 
the  latter  being  the  ultimate  product  of  oxidation.  The  higher 
oxide  is  reduced  to  the  lower  when  heated  with  metallic  copper. 
Cuprous  oxide  is  readily  dissolved  in  all  proportions  by  molten 
copper.  Both  oxides  are  reducible  by  carbon  and  both  are  solu- 
ble in  mineral  acids. 

Sulphides. — There  are  two  sulphides  of  copper,  analogous  to 
the  oxides.  Cupric  sulphide  (CuS)  is  the  form  in  which  the 
metal  is  generally  combined  in  its  ores.  One-half  of  this  sul- 
phur is  evolved  at  a  moderately  high  temperature,  so  that  roasted 
ere  contains  cuprous  sulphide  (Cu2S).  Upon  further  heating 
in  an  oxidizing  atmosphere  cuprous  sulphide  is  partially  converted 
into  the  oxides,  which  in  turn  react  with  the  sulphide,  liberating 
copper  and  sulphur  dioxide.  Under  certain  conditions  cuprous 
sulphide  is  changed  by  roasting  to  the  sulphate  ("sulphate  roast- 
ing"). When  roasted  with  salt  cuprous  and  cupric  chlorides 
are  formed  ("chloridizing  roasting"). 

Silica  reacts  readily  with  cuprous  oxide  at  furnace  tempera- 
tures, forming  a  liquid  slag.  From  cuprous  silicate  copper  may 
be  reduced  by  carbon,  and  cuprous  oxide  may  be  set  free  by  the 
substitution  of  a  stronger  base  such  as  ferrous  oxide  or  lime. 

Copper  is  precipitated  from  aqueous  solutions  of  its  salts  by 
iron,  aluminum  and  zinc,  and  by  the  electric  current. 

PRELIMINARY  TREATMENT 

The  processes  for  smelting  copper  differ  considerably  on  ac- 
count of  the  character  of  the  ores  and  other  conditions  in  dif- 


174  METALLURGY 

ferent  localities.  But  practically  all  processes  are  similar  in 
theory,  being  universally  applied  to  sulphide  ores.  It  is  not 
practicable  to  separate  copper  from  the  ore  by  a  single  opera- 
tion. There  is  usually  a  large  amount  of  sulphur  to  be  eliminat- 
ed, and  the  large  excess  of  mineral  matter  present  would  yield 
an  overwhelming  quantity  of  slag  to  entangle  the  metal.  The 
practice  is  to  first  roast  the  ore,  thereby  getting  rid  of  a  large 
part  of  the  sulphur  and  other  volatile  matter,  and  then  to  fuse  the 
•ore  under  proper  conditions,  when  the  heavier,  metal-bearing 
portion  separates  from  the  barren  gangue  by  liquation.  This 
•concentrated  material  is  a  mixture  of  copper  and  iron  sulphides 
and  is  known  as  matte  or  regulus.  A  concentrate  in  which  the 
sulphur  is  replaced  by  arsenic  is  called  a  speiss.  Matte  is  further 
treated  by  fusion  in  an  oxidizing  atmosphere,  the  iron  being 
oxidized  first  and  fluxed  out  by  means  of  silica,  leaving  the  en- 
riched sulphide  of  copper.  This  is  known  as  blue  metal  if  it 
still  contains  a  considerable  amount  of  iron  and  about  65  per 
cent,  of  copper.  White  metal  is  almost  pure  cuprous  sulphide, 
and  contains  75  per  cent.,  or  more,  of  copper.  Upon  further 
fusion  in  an  oxidizing  atmosphere  metallic  copper  is  obtained. 

It  will  be  seen  that  the  processes  now  to  be  studied  are  based 
upon  two  facts;  ist,  that  copper  has  a  stronger  affinity  for  sul- 
phur than  the  other  metals  associated  with  it  have;  2nd,  that 
copper  being  oxidized  reacts  on  its  own  sulphide  with  the  libera- 
tion of  metallic  copper.  The  preliminary  treatment  of  the  ore  con- 
sists principally  in  roasting.  This  is  done  in  several  ways  and 
will  be  described  at  length. 

Heap  Roasting. — This  is  the  cheapest  way  in  which  ores  are 
roasted.  It  requires  the  least  amount  of  fuel  and  the  minimum 
expenditure  of  labor,  but  it  is  not  adaptable  to  all  ores  and  is 
open  to  several  objections.  The  ore  must  be  for  the  most  part 
in  lump  form,  and  should  contain  at  least  15  per  cent,  of  sul- 
phur. With  ores  lower  in  sulphur  it  is  necessary  to  mix  fuel 
through  the  heap  to  produce  the  necessary  amount  of  heat. 
While  heap  roasting  may  be  very  efficient,  it  requires  great  care 
both  in  the  building  and  firing  of  a  heap  to  turn  out  a  product 
that  is  up  to  present  day  requirements.  The  consequences 


COPPER  175 

of  setting  free  so  much  sulphurous  acid  are  to  be  considered. 
In  many  places  the  practice  is  prohibited  by  law. 

The  site  for  the  operation  should  be  sheltered  from  the  winds, 
which  would  cause  uneven  burning.  A  spot  is  generally  chosen 
which  is  large  enough  to  accommodate  a  number  of  heaps.  The 
heap  is  built  upon  a  foundation  of  rock  or  slag.  The  dimensions 
of  a  heap  are  determined  largely  by  the  character  of  the  ore. 
According  to  Peters  a  heap  24  by  40  feet  at  the  base  and  6  feet 
high  contains  about  240  tons  of  ordinary  ore.  In  building  a 
heap  a  layer  of  wood  is  first  placed  for  kindling  the  ore.  Sev- 
eral chimneys  are  set  up  along  the  middle  line  of  the  foundation, 
and  canals  are  left  in  the  layer  of  wood  leading  from  the  chimneys 
to  the  outside.  This  is  done  to  facilitate  the  combustion  of  the 
ore  by  creating  a  draft  and  drawing  air  into  the  heap.  The  large 
lumps  of  ore  are  placed  upon  the  wood,  and  the  heap  is  finished 
with  smaller  lumps  and  covered  with  fine  ore.  A  portion  of  the 
top  and  a  space  around  the  bottom  are  left  uncovered  so  that 
the  heap  will  be  open  enough  for  the  circulation  of  air. 

The  heap  may  be  fired  at  the  outer  openings  of  the  canals,  or 
in  the  chimneys.  The  aim  is  to  effect  a  uniform  kindling  of 
the  entire  heap.  During  the  first  twenty-four  hours  of  the  burn- 
ing the  products  of  distillation  from  the  wood  are  driven  off 
with  some  sulphur,  producing  exceedingly  foul  odors.  After 
the  wood  has  been  consumed  the  sulphur  becomes  the  fuel  and 
the  combustion  continues.  The  surface  of  the  heap  is  examined 
at  intervals  for  indications  of  local  overheating.  This  is  shown 
by  the  fumes,  which  issue  from  every  opening,  becoming  thin- 
ner and  rising  more  rapidly.  The  combustion  is  checked  in  such 
cases  by  throwing  on  some  fine  ore.  In  case  the  combustion 
is  too  much  retarded  at  any  point  vents  are  made  in  the  covering 
to  admit  air.  The  time  required  for  roasting  a  heap  of  the 
above  dimensions  is  about  70  days,  depending  upon  the  com- 
position of  the  ore  and  the  weather.  For  the  recovery  of  cop- 
per sulphate  from  heap  roasting  see  p.  200. 

Stall  Roasting. — Stalls  are  partial  enclosures  in  which  the 
ore  is  protected  from  the  wind  while  burning.  The  common 
form  is  rectangular,  three  of  the  sides  being  permanent  masonry.- 


176  METALLURGY 

The  floor  is  paved  and  the  top  is  left  open.  A  number  of  stalls 
are  built  adjacent,  with  the  openings  on  the  same  side,  an  ar- 
rangement which  facilitates  the  handling  of  the  ore.  For  the 
building  material  either  brick  or  stone  is  used.  Stall  roasting 
may  be  considered  a  step  toward  furnace  roasting,  though  no 
more  advantage  can  be  claimed  for  the  practice  than  that  of 
roasting  in  heaps  so  far  as  the  quality  of  the  product  is  concern- 
ed. Stalls  have  not  been  favored  in  this  country. 

Furnace  Roasting. — The  largest  proportion  of  ore  by  far  is 
now  roasted  in  furnaces.  All  classes  of  ores  may  be  roasted 
more  completely  and  in  the  manner  desired  in  furnaces.  Many 
styles  of  furnaces  are  in  use,  each  kind  being  chosen  for  the 
particular  grade  or  quality  of  ore  to  be  treated.  The  ore  must 
in  all  cases  be  in  the  pulverulent  form.  Rock  breakers  are  used 
for  crushing  the  large  lumps  and  the  finer  crushing  is  done  in 
stamp  and  roller  mills.  A  description  of  crushing  machinery  is 
given  in  Chapter  VI.  The  furnaces  in  use  for  roasting  ores 
may  be  classed  as  hand  reverberatory,  mechanical  reverbera- 
tory  and  shaft  furnaces. 

Hand  Reverberatory  Furnaces. — This  style  of  furnace  is  alter- 
ed to  suit  different  grades  of  ore.  The  essential  parts  are  the 
flat  hearth  for  receiving  the  charge;  the  grate,  which  is  separat- 
ed from  the  hearth  by  a  bridge  wall;  the  side  working  doors, 
giving  ready  access  to  the  hearth;  the  low,  arched  roof,  con- 
structed so  as  to  reflect  heat  upon  the  hearth,  and  the  tall  flue. 
The  furnace  is  commonly  constructed  with  two  or  more  hearths 
at  different  levels,  the  ore  being  raked  from  one  down  upon  the 
other,  or  the  hearth  is  elongated  on  the  same  level  for  several 
times  its  width  as  shown  in  Fig.  62. 

In  the  operation  of  this  furnace  the  ore  is  charged  on  the 
upper  hearth,  or  at  the  end  farthest  from  the  grate,  and  is  raked 
successively  to  the  hearths  or  portions  of  the  hearth  nearer  the 
grate.  The  temperature  of  the  roasting  is  therefore  gradually 
raised,  since  the  portion  of  the  hearth  nearest  the  grate  is  the 
hottest.  The  ore  is  left  on  the  last  hearth  until  it  is  roasted 
"dead,"  and  then  drawn.  A  furnace  with  two  or  three  hearths 
is  preferred  for  ores  containing  more  than  10  per  cent,  of  sul- 


COPPER 


m 


m 


phur,  and  if  the  sulphur  content  exceeds  20  per  cent,  the  four 
hearth  furnace  is  found  most  satisfactory.  The  advantage  of 
the  long  hearth  lies  both  in  economy  and  effectiveness  of  roast- 


178  METALLURGY 

ing,  as  may  be  understood  from  what  has  been  said  about  roast- 
ing. If  ore  rich  in  sulphur  is  charged  upon  a  hearth  that  is 
hot  enough  to  kindle  it,  the  ore  roasts  of  itself,  and  the  necessary 
heat  is  generated  by  the  burning  sulphur. 

Mechanical  Furnaces. — The  cost  of  operating  the  hand  re- 
verberatory  furnace  is  rather  high  on  account  of  the  labor  re- 
quired. The  labor  of  moving  the  ore  on  the  hearth  and  of  dis- 
charging it  from  the  furnace  is  dispensed  with  by  the  use  of 
power-driven  stirrers  or  furnaces  which  are  rotated  mechanical- 
ly. 

The  Brown  roaster  represents  the  type  of  furnace  in  which  the 
ore  is  stirred  mechanically  on  a  stationary  hearth.  Fig.  63 
shows  the  plan  and  section  of  the  "Horseshoe"  form  of  Brown 
roaster.  The  circular  hearth  is  heated  by  three  fire-places,  one 
of  which  is  shown  in  the  illustration  as  an  enlarged  section.  As 
shown  in  the  sectional  view,  A-B,  spaces  are  partitioned  on 
both  sides  of  the  hearth.  The  partition  walls  are  projected 
from  the  roof  and  floor  of  the  furnace,  and  a  horizontal  slot, 
extending  the  entire  length  of  the  hearth,  is  left  between  the 
parts  projected.  In  these  spaces  or  conduits,  exterior  to  the 
hearth,  rails  are  laid,  and  upon  these  two  or  more  carriages 
are  driven  by  means  of  a  wire  rope.  The  carriages  support  the 
arms  of  the  stirrers  which  pass  through  the  slotted  walls.  The 
stirrers  are  armed  with  shoes  which  plow  through  the  thin 
layer  of  ore  on  the  hearth  and  move  it  toward  the  fire-boxes. 
The  path  of  the  stirref  carriages  is  a  complete  circle,  the  space 
between  the  flue  and  the  first  fire-box  being  uncovered.  This 
space  in  the  outer  air  serves  to  cool  the  carriages.  The  ore  is 
fed  into  the  furnace  by  an  automatic  device,  outlined  in  the 
drawing.  The  smoke  is  led  into  a  tall  chimney,  the  location  of 
which  is  also  shown. 

The  Bruckner  and  the  White-Howell  furnaces  are  common 
representatives  of  the  -rotating  type.  They  consist  of  brick-lined 
cylinders,  mounted  upon  friction  rollers  between  a  fire-place  and 
flue.  The  cylinders  are  slowly  revolved  while  an  oxidizing 
Hame  passes  into  them,  coming  into  intimate  contact  with  the 
constantly  moving  ore.  The  Bruckner  furnace  is  charged  from 


COPPER 


179 


hoppers  supported  directly  over  the  cylinder,  the  ore  being  charged 
and  removed  intermittently  through  manholes  in  the  side  of  the 
cylinder.  At  seme  plants  a  number  of  furnaces  are  operated  in 


i8o 


METALLURGY 


line,  and  the  fire-box  is  carried  on  a  truck  which  runs  on  a 
track  at  right  angles  to  the  axes  of  the  cylinders.  After  ignit- 
ing the  ore  in  one  cylinder  the  fire-box  is  moved  to  another, 
leaving  a  free  access  of  air  to  continue  the  roasting  of  the  ignited 
ore. 

In  the  White-Howell  type  of  roaster  the  cylinder  is  slightly 
inclined  toward  the  fire-box.  The  ore  is  fed  in  automatically  at 
the  flue  end,  and  advanced  toward  the  fire-box  by  the  motion  of 


Fig.  64 — Herreshoff  Furnace.      (Nichols  Copper  Co.) 

the  cylinder.     The  roasted  ore  drops  between  the   end   of  the 
cylinder  and  the  fire-box  into  a  vault. 

Shaft  Furnaces  are  used  when  the  sulphur  from  the  ore 
is  to  be  recovered  for  the  manufacture  of  sulphuric  acid.  These 
vary  much  in  style  and  are  adaptable  only  to  ores  rich  in  sul- 
phur. All  of  the  improved  furnaces  have  mechanically 
operated  parts.  The  Herreshoff  furnace  is  of  recent  develop- 
ment though  it  has  found  considerable  application  for  the  treat- 


COPPER 


181 


ment  of  copper  and  iron  sulphide  ores,  especially  in  connection 
with  the  manufacture  of  sulphuric  acid.  As  shown  in  the  sec- 
tion and  elevation,  (Figs.  64  and  65)  the  furnace  is  cylindrical 
in  form.  It  is  lined  throughout  with  fire-brick.  Inside  the 
furnace  are  five  circular  shelves,  built  of  fire-brick  and  slightly 
arched  toward  the  center.  The  ore  is  fed  into  the  furnace  auto- 
matically from  a  hopper  at  the  top.  Beginning  with  the  upper- 
most there  are  alternately  peripheral  and  central  openings 


Fig.  65— Herreshoff  Furnace.     (Nichols  Copper  Co.) 

through  the  shelves  which  permit  the  ore  to  pass  downward  and 
the  gases  to  pass  upward.  A  large,  vertical  shaft  revolves  in 
the  center  of  the  furnace  and  carries  two  arms  over  each  shelf. 
Teeth  are  attached  to  the  arms  for  stirring  and  advancing  the 
ore.  The  teeth  are  set  at  such  angles  that  they  move  the  ore 
on  each  shelf  toward  the  openings.  After  passing  from  shelf 
to  shelf  the  ore  is  discharged  from  the  bottom  shelf  through  two 
openings  at  its  circumference.  The  shaft  carrying  the  stirrers 


1 82  METALLURGY 

is  hollow,  and  it  is  cooled  by  a  draft  of  air.  The  doors  on  the 
side  of  the  furnace  (Fig.  65)  give  access  to  the  shelves  and  stir- 
rers.  The  latter  are  replaced  with  new  ones  when  disabled  by 
the  heat  and  acid  gases.  After  once  igniting  it  the  ore  is  roasted 
without  fuel,  and  the  process  is  continuous. 

Chemistry  of  Roasting. — The  principal  reactions   which  take 
place  when  copper  ores  are  roasted  may  be  represented  thus : 

FeS2  +  02  =  FeS  +  SO, 

2CuS  -f  O,  =  Cu2S  -f  SO, 

FeS  -f  O3  =  FeO  -f  SO2 

S02  -f-  O    =  S03 
FeO  +  S03  =  FeSO, 
Cu2S  +  O3  ==  Cu2O  -f  SO2 
Cu2O  +  FeS  =  Cu2S  +  FeO 
Cu2O  -f-  2FeSO4  +  02  =  2CuS04    f  Fe2O3 

3FeO  -f  O  =  =  Fe304. 

No  elaborate  or  exact  information  has  been  gathered  covering 
the  many  changes  which  take  place  from  the  time  the  ore  is 
charged  until  it  is  withdrawn  from  the  furnace,  though  some 
very  valuable  data  has  been  obtained  from  the  analysis  of  the 
ore  at  different  stages  of  the  operation.  Iron  pyrites  is  the  first 
compound  to  give  off  sulphur.  Cupric  sulphide  also  decomposes 
at  a  comparatively  low  temperature,  giving  up  one  atom  of  its 
sulphur  and  yielding  cuprous  sulphide.  With  an  increase  in 
temperature  the  monosulphide  of  iron  is  converted  into  the 
protoxide.  This  is  either  oxidized  immediately  to  the  higher 
form  or  combined  with  any  acid  present.  The  formation  of  sul- 
phuric anhydride  is  believed  to  be  due  to  the  catalytic  action  of 
silica  or  other  inert  material  in  the  ore  with  sulphur  dioxide  and 
oxygen.  The  sulphate  of  iron  is  formed  in  considerable  quan- 
tity if  the  temperature  is  not  too  high.  This  is  largely  decom- 
posed by  cuprous  oxide,  copper  sulphate  resulting.  It  will  be 
seen  that  the  roasting  and  each  succeeding  operation  in  the 
smelting  process  depend  largely  upon  the  basic  properties  of 
copper.  Having  superior  affinity  for  sulphur  it  remains  in 
combination  with  this  element  as  the  iron  is  being  oxidized,  and 
being  fusible  in  this  form,  it  is  readily  separated  from  the 
gangue  or  slag  by  liquation  during  the  smelting  process. 


COPPER 

The  burning  of  the  sulphur  gives  rise  to  enough  heat,  in  most 
cases,  to  complete  the  roasting  without  the  addition  of  extrane- 
ous heat.  As  a  rule,  however,  in  practice  most  of  this  heat  goes 
to  waste.  In  the  heaps  the  roasting  is  generally  finished  without 
the  use  of  other  than  kindling  fuel,  and  in  all  furnaces  a  saving 
of  fuel  is  appreciated  from  the  fact  that  the  ore  burns  and  thus- 
raises  the  temperature  of  the  furnace.  This  subject  is  further 
studied  in  the  next  chapter. 


CHAPTER  XVIII 


COPPER  SMELTING 

Copper  smelting  comprises  two  or  more  distinct  operations. 
It  begins  with  the  fusion  of  the  oxidized  ore,  the  product  of  the 
first  operation  being  a  matte,  and  ends  with  the  oxidizing  fusion 
of  the  matte,  the  product  of  the  last  operation  being  unrefined 
copper.  The  entire  process  of  copper  smelting  was  formerly 
conducted  in  reverberatory  furnaces,  a  practice  which  is  still 
adhered  to  in  many  places,  but  the  blast  furnace  has  new  largely 
replaced  the  reverberatory.  Smelting  may  be  classed  accord- 
ing to  the  practice  as  reverberatory,  blast  furnace  and  pyritic 
smelting. 

REVERBERATORY  SMELTING 

This  process  was  developed  in  England  and  Wales,  and  has 
undergone  but  few  important  changes.  It  is  still  the  most  used 
process  in  Europe,  and  is  more  adaptable  to  some  grades  of  ore 
than  any  other.  Reverberatory  smelting  consists  of  a  series  of 
fusions  and  roastings,  each  roasting  eliminating  sulphur  and 
each  fusion  separating  matte  in  a  more  concentrated  form. 

Fusion  for  Matte. — For  this  operation  a  large  reverberatory 
furnace  is  used.  A  recently  built  furnace  for  matting  copper 
ores  is  shown  in  plan  and  elevation  in  Figs.  66  and  67.  The 
walls  of  the  lurnace  are  of  red  brick  and  the  lining  is  of  fire- 
brick. The  brick  work  is  held  together  by  steel  rails  and  tie- 
rods.  The  hearth  and  lower  walls  of  the  furnace  are  protected 
by  a  lining  or  fettling  of  sand.  The  pear-shaped  hearth  is  com- 
mon to  copper  smelting  furnaces.  Since  a  high  temperature  is 
required  in  this  furnace  the  fire-box  is  large  in  proportion  to 
the  hearth  area.1  The  furnace  is  provided  with  skimming  doors 
on  both  sides  for  removing  tne  slag,  and  a  tap-hole  for  drawing 
off  the  matte.  The  ore  is  charged  through  circular  openings  in 

1  Some  furnaces  are  equipped  with  air  heating  apparatus  which  facili- 
tates the  maintaining  of  the  temperature  desired. 


COPPER  SMELTING 


18=; 


COPPKR  SMELTING  187 

the  roof  of  the  furnace  from  three  double  hoppers.  The  coal 
is  likewise  let  into  the  fire-box  through  the  funnels  of  one  double 
hopper.  A  tall  chimney  carries  away  the  sulphurous  smoke  and 
maintains  a  steady  draft. 

The  charge  is  made  up  of  roasted  and  raw  ore,  slag  from  re- 
fining furnaces,  etc.,  mixed  to  produce  the  matte  and  slag  of  thp 
proper  compositions.  After  leveling  down  the  charge  the  tem- 
perature of  the  furnace  is  raised  rapidly.  Within  a  few  hours 
time  the  ore  is  completely  fused.  A  quantity  of  slag  is  formed 
and  a  portion  of  the  sulphur  is  evolved.  The  bath  is  well  rab- 
bled, and  after  it  becomes  tranquil  it  is  left  undisturbed  for  half 
an  hour  to  allow  the  matte  to  settle.  The  slag  is  then  skimmed 
off  through  the  working  doors,  and  the  matte  is  tapped.  Enough 
matte  is  left  in  the  furnace  to  protect  the  hearth  from  sudden 
cooling  and  from  the  corrosive  action  of  fresh  ore.  The  fer- 
rous oxide  and  other  bases  exert  a  constant  scorification  of  the 
hearth  lining  or  fettling,  and  this  must  be  frequently  renewed. 

Fusion  for  Blue  or  White  Metal. — If  the  matte  from  the  above 
operation  is  a  rich  one  it  may  be  converted  by  a  single  fusion  in- 
to white  metal,  otherwise  it  yields  the  intermediate  product,  blue 
metal.  If  very  poor  the  matte  is  roasted  before  fusion.  It  is 
first  granulated  by  running  it  into  water  directly  from  the  furnace, 
or  by  grinding  it  in  a  mill,  so  that  the  roasting  will  be  more  ef- 
fective. During  the  fusion  the  iron  is  fluxed  out  by  adding  some 
silicious  slag  from  a  previous  operation,  or  by  means  of  raw  ore 
or  other  material.  The  furnace  used  for  the  fusion  of  mattes  is 
similar  in  construction  to  the  one  above  described.  It  is  gen- 
erally smaller  and  the  fire-place  is  larger  in  proportion  to  the 
hearth.  A  higher  temperature  is  employed  than  is  needed  in 
the  fusion  for  matte,  but  the  operation  is  very  similar.  At  the 
end  of  the  operation  the  enriched  copper  sulphide  forms  the  lower 
layer  in  the  bath,  and  the  oxidized  slag  floats  on  top.  After 
skimming  the  slag  the  product  is  tapped  and  run  into  molds. 

Fusion  for  Blister  Copper. — This  operation  is  conducted  in  a 
furnace  of  somewhat  the  same  construction  as  the  matte  furnace, 
except  for  the  increased  grate  capacity.  The  hearth  is  well 
soaked  before  use  with  high  grade  matte,  and  upon  this  a  layer 
of  copper  is  melted.  This  protects  the  hearth  from  the  corro- 


1 88  METALLURGY 

sive  action  of  the  charge.  The  white  metal  is  charged  in  the 
form  of  pigs,  and  the  temperature  is  raised  slowly,  air  being 
freely  admitted.  The  oxidation  proceeds  rapidly,  and  the  es- 
cape of  sulphur  dioxide  causes  "boiling"  after  the  bath  has  be- 
come liquid.  A  much  smaller  amount  of  slag  is  formed  than  in 
the  preceding  operation,  and  the  slag  is  much  richer  in  copper. 
This  is  skimmed  from  time  to  time.  When  tests  show  the 
proper  degree  of  purity  the  copper  is  tapped  and  run  into  molds, 
or  transferred  at  once  to  the  refining  furnace.  Metal  that  is  al- 
lowed to  cool  becomes  covered  with  blisters  from  the  escaping 
sulphur  dioxide — hence  the  term  "blister  copper."  There  is  one 
per  cent,  or  more  of  impurity  in  reverberatory  smelted  copper. 
Chemistry  of  Reverberatory  Smelting. — The  separation  of  the 
matte  from  the  ore  gangue  is  largely  mechanical.  The  most 
important  reactions  are  in  the  fluxing  of  the  iron  oxide  by 
silica — 

FeO  4-  SiO2  =  FeO.SiO2. 

Of  course  the  same  reactions  that  occur  during  the  roasting  are 
largely  repeated  here.  The  final  reactions  by  which  copper  is 
liberated  may  be  expressed  thus — 

Cu2S  +  03  ==  Cu20  +  S02 
Cu2S  +  2Cu20  ==  6Cu  +  S02. 

The  following  table,  prepared  by  E.  D.  Peters,  Jr.,  from  his 
own  experiments,  shows  the  rate  of  matte  oxidation  in  rever- 
beratory furnaces. 

Table  of  Matte  Concentration  by  Oxidation  Fusion — Percentages  of  Copper 
in  Fractions  Omitted. 


Char- 
ged. 

Mel- 
ted. 

No.  of  Hours  in  Furnace. 

O 

5 

6 

7 

8 

10  12 

14  16 

18  20 

22  24  26  28 

3°  32 

34  36  48 

16 

16 

17 

16 

19 

20   20 

21   22 

21 

23 

23 

25  29 

21 

23 

22 

25 

27 

27 

33 

37- 

i;4i 

39 

41 

41 

44 

49 

45' 

47 

53 

54 

58 

50 

55 

57 

59 

61 

61 

64 

58 

62 

62 

62 

61 

61  62 

65 

65 

67  68 

63 

67 

70 

72 

75 

78 

84 

69 

73 

73 

74 

74 

77  78 

77  82 

85 

89 

94 

98 

74 

82 

84 

88 

94 

99 

80 

86 

89 

93 

98 

86 

94 

99 

92 

96 

96 

98 

99 

99 

96 

98 

99 

COPPER  SMELTING  189 

Composition  of  Copper  and  Slag  in  Roasting-Smelting  for  Blister  Copper. 

Welsh  "Roaster"  Slag.  Kaafiord. 

Silica 47.5  36.0 

Protoxide  of  Iron 28.0  7.0 

Alumina 3.0  6.0 

Cuprous  Oxide 16.9  43.2 

L/ime 2.7 

Magnesia 0.8 

Nickel  and  Cobalt  Oxides 0.9  4.9 

Oxide  of  Tin 0.3  0.6 

Oxide  of  Zinc 2.0  3. 2 

Welsh  Blister  Copper.  Kaafiord. 

Copper 99.2-99.4 

Iron 0.7-0.8  0.1-0.2 

Nickel  and  Cobalt...      0.3-0.9  0.2-  0.3 

Zinc 0.0-0.2 

Tin 0.0-0.7  

Arsenic 0.4-1.8 

Sulphur 0.1-6.9  o.i-  o.i 2 

BLAST  FURNACE  SMELTING^ 

Blast  furnaces  for  smelting  copper  ores  were  first  used  in 
Germany.  They  have  been  successfully  introduced  in  all  im- 
portant copper  producing  countries,  and  have  been  specially 
favored  in  the  United  States.  The  evolution  of  the  copper 
furnace  has  been  quite  as  remarkable  as  that  of  the  iron  furnace, 
though  no  doubt  a  great  deal  has  been  borrowed  from  the  iron 
smelter.  There  are  a  number  of  styles  of  furnaces  in  use  for 
the  treatment  of  copper  ores,  the  differences  being  brought  about 
by  the  varying  character  of  the  ores,  fuel  and  other  local  condi- 
tions. 

Fig.  68  represents  the  round  style  of  furnace  commonly  used 
in  the  West.  It  is  built  of  steel  plates,  rivetted  together,  and  is 
supported  on  four  cast  iron  columns.  The  annular  base  plate 
is  also  of  cast  iron.  In  the  center  of  this  is  a  larj  e,  circular 
opening  which  is  closed  by  two  drop  doors.  The  crucible  is 
lined  with  fire-brick,  and  the  bottom  is  tamped  with  clay.  The 
walls  above  the  crucible  are  water-jacketed  almost  t.  the  charg- 
ing door.  These  jackets  consist  of  outer  and  inner  walls  of  steel 
plates  rivettecl  or  welded  together  to  form  a  shell  through  which 
the  water  is  circulated.  The  inner  wall  of  the  jacket  is  often 


Fig.  68— Round  Type  of  Blast  Furnace.     (Allis-Chalmers  Co.)' 


Fig.  69— Rectangular  Type  of  Blast  Furnace.     (Allis-Chalmers  Co.) 


COPI'ER  SMELTING  19 r 

made  of  copper,  since  copper  is  not  so  readily  corroded  by  the 
charge  as  steel  is.  At  the  top  the  furnace  walls  are  contracted 
to  form  a  hood,  which  terminates  in  the  stack.  The  out- 
line in  the  region  of  the  hood  shows  the  location  of  the  charg- 
ing door. 

The  blast  is  furnished  by  means  of  a  positive  blower  of  the 
rotary  type.  It  is  received  in  a  box  surrounding  the  furnace, 
and  is  delivered  to  the  charge  through  tuyeres  which  pierce  the 
water-jacket.  Access  to  the  tuyeres  is  gained  from  the  outside 
through  small  openings  in  the  blast  box.  The  openings  are 
closed  with  sliding  doors.  The  location  of  the  slag  spout  is 
shown  in  section,  and  the  matte  spout  is  shown  in  outline.  These 
furnaces  are  used  both  with  and  without  the  forehearth. 

In  order  to  increase  the  capacity  of  the  copper  cupola  the  cru- 
cible is  widened.  Since  it  is  necessary  that  the  blast  penetrate 
the  charge  fully,  the  limit  to  which  the  crucible  may  be  widened 
is  soon  reached.  It  may,  however,  be  extended  in  one  direction, 
leaving  the  opposite  tuyeres  the  same  distance  apart.  This  has 
been  done  in  the  development  of  the  elliptic  and  rectangular 
styles  of  furnace.  The  photographic  view  (Fig.  69)  shows  the 
rectangular  style  of  furnace.  This  furnace  is  water-jacketed  in 
double  tiers,  the  upper  jackets  extending  below  the  tuyere  line. 
.Both  the  upper  and  lower  jackets  are  supported  from  a  mantle 
frame  of  heavy  beams  and  channels  carried  on  four  cast  iron 
columns.  The  tap-holes  and  spouts  are  shown  at  the  front  side 
and  end  of  the  furnace.  The  slag  spout  is  of  bronze  and  water- 
jacketed.  The  bottom  plate  is  supported  on  jack-screws  which 
are  carried  on  a  truck.  This  arrangement  facilitates  the  re- 
moval of  the  bottom  when  it  becomes  necessary.  In  the  older 
-furnaces  the  base  plate  is  supported  on  short  columns.  The 
furnace  walls  above  the  water-jackets  are  of  brick,  reenforced 
as  shown.1  The  hood  is  made  of  cast  iron  or  steel,  and  is  pro- 
vided with  two  openings  for  charging.  The  hood  carries  the 
stack  and  downtake  pipes,  which  are  of  steel.  The  blast  pipes 
and  water  connections  are  easily  traceable  in  the  illustration. 

1  Brick  walls  are  less  destructible  than  metal  in  this  part  of  the  furnace, 
since  the  metal  is  corroded  by  sulphates  in  the  ore. 


192  METALLURGY 

Forehearths. — Copper  blast  furnaces  are  commonly  equipped 
with  forehearths,  the  duty  of  which  is  to  take  the  slag  and  matte 
from  the  furnace  as  fast  as  it  accumulates.  In  other  words,  the 
forehearth  is  an  outside  crucible  which  relieves  the  inner  crucible 
or  furnace  hearth  of  the  scorifying  melt.  The  forehearth  is  lined 
with  fire-brick  or  water-jacketed,  and  is  provided  with  a  spout 
at  the  top  for  the  overflow  of  slag  and  a  tap-hole  for  drawing  off 
the  matte.  It  is  usually  kept  covered  to  prevent  the  rapid  cool- 
ing and  crusting  of  the  contents.  The  forehearth  is  mounted  on 
wheels  so  that  it  can  quickly  be  replaced  by  a  new  one  when 
disabled. 

The  Process. — When  a  furnace  is  to  be  blown  in  it  is  never 
begun  with  the  regular  charges.  The  first  charges  contain  a  rather 
large  proportion  of  coke,  and  the  rest  is  principally  slag  from 
previous  running.  When  the  temperature  is  high  enough  ore 
is  introduced,  and  is  increased  with  each  charge  until  the  regular 
burden  is  reached.  The  furnace  is  charged  continuously  as  in 
iron  smelting,  and  the  blast  pressure  is  regulated  to  suit  the  con- 
ditions of  working.  Limestone  is  added  as  a  flux.  Much  skill 
is  required  in  maintaining  the  proper  mixture  of  ore  and  flux, 
so  that  the  slag  will  contain  a  minimum  amount  of  copper.  The 
fuel  is  gaged  to  supply  sufficient  heat  and  to  permit  of  some 
oxidation. 

The  matte  and  slag  run  out  of  the  furnace  as  fast  as  they  are 
melted  and  collect  in  the  forehearth,  where  they  separate  by 
gravity  in  layers.  The  slag  runs  away  through  the  spout  pro- 
vided, and  is  usually  rejected.  The  matte  is  tapped  at  inter- 
vals into  ladles  and  taken  away  for  further  treatment. 

The  principles  of  blast  furnace  and  reverberatory  smelting 
do  not  differ  materially.  In  blast  furnace  practice  the  charges 
are  calculated  more  closely,  so  that  the  mixture  will  throw  down 
the  proper  grade  of  matte.  Blast  furnace  slags  generally  contain 
less  copper,  and  the  tenor  of  copper  in  the  mattes  is  lower.  A 
great  deal  of  importance  is  attached  to  the  selection  of  ore  for 
the  charges.  If  there  is  a  large  quantity  of  fully  oxidized  ore  in 
stock,  raw  sulphide  is  mixed  with  it,  lest  copper  be  fully  reduced 
and  carried  into  the  slag.  On  the  other  hand,  care  is  taken  not 


OF  THE 

[UNIVERSITY 


Fig.  70— Bisbee  Converter.     (Allis-Chalmers  Co.) 


COPPER  SMELTING  195 

to  allow  too  much  sulphur  in  the  charge,  since  that  would  carry 
down  more  iron  into  the  matte,  rendering  it  too  low  in  copper.  It 
is  the  aim  to  make  as  uniform  a  grade  of  matte  as  possible,  and 
the  furnaces  are  usually  pushed  to  their  full  capacity.  Up  to  a 
certain  limit,  the  greater  the  blast  pressure,  the  more  rapid  will 
be  the  melting,  and  the  lower  will  be  the  consumption  of  fuel 
per  ton  of  matte. 

The  disposal  of  the  matte  as  fast  as  it  is  melted  greatly  length- 
ens the  life  of  the  furnace  hearth.  It  has  been  found  best  in 
most  American  works  to  aim  at  a  matte  containing  45  to  55  per 
cent,  of  copper.  The  effort  is  made  to  concentrate  any  gold 
and  silver  into  the  matte  so  that  they  will  be  recovered  with  the 
copper,  and  to  discard  as  much  of  the  slag  as  possible.  This 
may  be  done  if  so  little  copper  passes  into  the  slag  that  it  is 
worthless. 

The  example  given  on  next  page  may  be  taken  as  representa- 
tive of  modern  blast  furnace  practice.1 

Treatment  of  Matte  in  Bessemer  Converters. — This  process  was 
invented  in  1880  by  John  Hollway,  of  England,  and  was  intro- 
duced into  the  United  States  shortly  afterwards.  The  idea  was 
borrowed  from  Bessemer's  patent,  the  general  form  of  the  con- 
verter and  the  handling  of  it  being  similar. 

The  Bisbee  converter,  representing  an  improved  style,  is  shown 
in  Fig.  70.  This  is  built  in  the  form  of  a  short  cylinder,  the 
cuter  shell  of  which  is  of  steel  plates  and  the  lining  of  crushed 
quartz  or  silica  in  other  form.  The  cylinder  is  mounted  hori- 
zontally on  four  friction  rollers,  and  is  rotated  by  means  of  a 
vertical  rack  and  hydraulic  power.  The  rack  is  held  against  a 
spur  gear  on  the  head  of  the  vessel.  The  blast  conduit,  attached 
to  the  converter  shell,  is  shown  in  the  illustration.  This  is  con- 
nected with  the  blast  pipe  from  the  blowing  engines  in  line  with 
the  axis  of  the  converter,  so  that  it  does  not  interfere  with 
the  rotation  of  the  latter.  Since  the  level  of  the  tuyere  openings 
1  Peters-"  Copper  Smelting,"  p.  367. 
7 


194 


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COPPKR  SMELTING  195 

is  above  the  bottom  of  the  converter,  the  metal  that  settles  to 
the  bottom  during  a  blow  is  not  disturbed  by  the  blast.3 

The  Process. — Before  charging  the  first  time  the  converter  is 
heated  by  means  of  a  coke  fire.  It  is  turned  down  to  the  hori- 
zontal position  and  the  molten  matte  is  run  in.  At  the  same  time 
a  light  blast  is  turned  on,  and  this  is  increased  to  the  full  pres- 
sure as  the  converter  is  raised  to  the  upright  position.  Desul- 
phurization  begins  at  once  and  proceeds  rapidly  as  shown  by  the 
rise  of  a  bluish-white  flame  from  the  mouth  of  the  converter. 
The  blow  is  continued  until  all  the  iron  is  oxidized  and  fluxed, 
a  point  which  can  only  be  ascertained  from  experience.  The  blower 
is  guided  by  the  appearance  of  the  flame,  the  border  of  which  is 
greenish  while  the  iron  is  being  oxidized.  The  appearance  of 
the  flame  is  altered  by  such  volatile  impurities  as  lead,  zinc  and 
arsenic.  If  much  slag  forms  it  is  poured  off  before  the  blow  is 
finished.  Being  so  much  lighter  than  the  copper  sulphide  the 
slag  separates  in  a  distinct  layer,  and  it  is  poured  off  by  tilting 
the  vessel.  The  slag  generally  retains  too  much  copper  to  be 
discarded,  and  it  is  returned  to  the  matte  smelter.  The  residue 
in  the  converter  is  almost  pure  cuprous  sulphide.  The  blowing 
is  continued  until  the  sulphur  is  practically  removed,  leaving1 
the  copper  from  97  to  99  per  cent.  pure.  The  copper  is  cast  into 
pigs  or  into  anode  plates,  according  to  the  way  in  which  it  is 
to  be  refined. 

In  theory  the  Bessemer  process  is  similar  to  the  other  pro- 
cesses  by  which  blister  copper  is  made.  The  reactions  of  course 
take  place  much  more  rapidly  in  the  converter,  since  by  blowing 
air  through  the  molten  matte  the  entire  charge  is  acted  on  at 
once.  Instead  of  silicious  ore  as  is  added  in  the  reverberatory 
process,  the  supply  of  silica  is  drawn  from  the  converter  lining. 
If  the  charge  of  matte  is  low  in  copper  the  slag  will  of  course 
be  great  in  bulk.  It  is  high  in  silica  and  very  liquid.  A  rich 
matte  yields  a  small  quantity  of  thin  slag,  rich  in  iron.  A  quan- 

1  Copper  converters  are  universally  side-blown,  since  bottom  blowing 
would  oxidize  the  metallic  copper  before  the  oxidation  of  the  matte  was 
complete. 


METALLURGY 


(I) 

l)                                              21  6 

(2) 

c«  o 

O°'u 

jo  4 

57-9 

7.8 

tity  of  dnst  passes  out  of  the  mouth  of  the  converter  with  the 
flame.  This  contains  the  oxides  of  such  volatile  impurities  as 
lead,  zinc,  arsenic,  etc.,  some  copper  and  not  infrequently  gold 
and  silver.  The  higher  the  percentage  of  volatile  matter  the 
greater  will  be  the  loss  of  precious  metals.  Peters  gives  the 
following  analyses  of  flue  dust  from  two  different  works : 


Silver  (oz.  per  ton) 
Copper  (per  cent. 
Lead 
Zinc          " 


The  time  required  for  converting  a  55  per  cent,  matte  is  about 
one  hour. 

The  following  analyses,  given  by  W.  R.  Vanliew,  show  the 
rate  of  oxidation  in  a  Bessemer  charge.1 

Time 

Copper  per  cent. 

Iron 

Sulphur    per  cent. 

Zinc 

Arsenic       ' ' 

Antimony  " 

Silver  ounce 

Gold 

The  Bessemer  process  is  now  firmly  established,  though  it  is 
likely  still  to  undergo  some  important  changes.  The  practice 
has  grown  considerably  within  recent  years  in  spite  of  serious 
difficulties  in  the  way  of  improvements.  One  of  the  most  seri- 
ous objections  to  it  lies  in  the  cost  of  repairs.  The  attempt  has 
been  made  to  substitute  a  more  durable  material  for  the  lining, 
thus  doing  away  with  the  expensive  practice  of  renewing  the 
lining  of  crushed  quartz.  Basic  linings  have  been  tried,  the 
necessary  silica  being  added  to  the  charge,  but  so  far  no  practical 
results  have  been  gained  from  these  experiments. 
1  Trans.  Amer.  Inst.  Min.  Eng.,  34,  418. 


;               Cupola  Tap 

10  Min. 

20  Min. 

30  Min. 

40  Min. 

70  Min. 
Blister 

Copper 

nt.  49.72 

50.20 

56.88 

64.60 

76.37 

99.120 

'     ••••     23.31 

23-I5 

17.85 

10.50 

2.40 

0.038 

cent...     21.28 

20.95 

19-74 

18.83 

16.30 

0-159 

"     ..       1.19 

1.  2O 

0.84 

0.70 

0-45 

0.090 

"     -.       o.n 

0.09 

0.08 

0.08 

0.08 

0.0012 

"     «.       0.14 

A  A    OCi 

0.12 
42   QO 

0.10 

C  T      AQ 

0.13 

rr  »O 

0.13 
*7O  OO 

O.OO6 

r\f\   $\C\C\ 

0  Tfi 

q.z.yu 
O-  T/i 

0  1  .^.V 

O.2O 

GO'00 
O  2/1 

O.72 

yLJ.OvJU 

n  7^0 

COPPER  SMELTING  IQ7 

PYRITIC  SMELTING 

The  term  pyritic  smelting  refers  to  those  methods  of  smelting 
ores  in  which  no  fuel  is  used  save  the  sulphur  which  the  ore  con- 
tains. As  has  been  stated,  all  processes,  to  a  certain  extent, 
utilize  the  heat  from  the  oxidation  of  the  sulphur  in  the  ore  or 
rnatte,  but  additional  heat  has  been  supplied  from  extraneous 
sources  in  all  processes  heretofore  studied.  Theoretically,  it  is 
possible  to  smelt  some  ores  to  the  production  of  blister  copper 
without  extra  fuel,  and  in  practice  this  has  been  accomplished  to 
the  extent  of  reducing  the  fuel  cost  to  insignificance.  Copper 
metallurgists  have  devoted  a  great  deal  of  attention  and  energy 
of  late  years  toward  the  perfection  of  such  a  process,  and  much 
has  been  gained  as  the  result  of  experimental  practice. 

A  blast  furnace  is  employed  in  pyritic  smelting,  and  as  a  rule, 
the  blast  is  preheated.  A  small  amount  of  coke  is  added  to  the 
charge,  as  occasion  requires,  and  the  process  is  conducted  sim- 
ilarly to  ordinary  blast  furnace  smelting,  for  the  production  of 
matte.  The  matte  is  treated  by  the  Bessemer  process,  which  is 
in  itself  "pyritic  smelting." 

Pyritic  smelting  has  been  found  especially  adaptable  to  rich 
sulphide  ores  bearing  gold  and  silver. 

The  Elimination  of  Impurities  from  Copper  Ores  During 
Smelting. — A  complete  study  of  the  metallurgy  of  copper  would 
involve  not  only  the  processes  by  which  copper  itself  is  extracted, 
but  also  those  by  which  various  other  metals,  associated  with 
copper  ores,  are  recovered.  For  example,  some  ores  carry  nickel 
as  well  as  copper  in  workable  quantity,  and  it  is  not  infrequent 
that  gold  and  silver  are  present  in  sufficient  amounts  to  justify 
more  expensive  methods  of  treating  the  ores  in  order  to  recover 
them.  Furthermore,  there  are  often  objectionable  impurities 
in  copper  ores  which  require  special  care  for  their  removal.  The 
most  important  of  the  foreign  elements  met  with,  and  their  be- 
havior during  the  smelting  are  summarized  below. 

Silicon. — This  element  occurs  as  silica  and  silicates  in  the  ore. 
It  is  fluxed  (as  silica)  by  any  basic,  metallic  oxides  present,  lime 


IQ8  METALLURGY 

* 

being  added  as  a  special  flux  to  prevent  its  combination  with 
cuprous  oxide.  In  the  blast  furnace  some  silicon  is  reduced  and 
this  may  escape  oxidation  and  be  found  in  the  blister  copper. 

Sulphur,  owing  to  its  affinity  for  copper,  is  not  eliminated 
until  the  concentrated  cuprous  sulphide  is  obtained.  It  is  finally 
separated  by  oxygen  at  the  high  temperature  of  the  converter 
or  the  reverberatory  furnace. 

Iron  exists  chiefly  as  a  sulphide  in  the  ore.  It  mixes  as  such 
with  cuprous  sulphide  in  the  matte  smeltery.  In  an  oxidizing 
atmosphere  iron  parts  with  its  sulphur  at  a  comparatively  low 
furnace  temperature,  and  it  is  readily  fluxed  and  separated  from 
cuprous  sulphide  by  means  of  silica.  A  small  amount  of  iron  is 
reduced,  and  alloyed  with  the  copper. 

Arsenic  should  be,  for  the  most  part,  removed  from  the  ore 
(luring  the  roasting,  being  volatile.  Most  of  the  arsenic  that  is 
left  in  the  ore  is  retained  by  the  copper,  either  as  arsenide  or 
arsenate. 

Antimony  is  similar  in  its  behavior  to  arsenic.  It  is  concen- 
trated like  arsenic  in  the  matte  or  speiss.  Antimony  is  less 
volatile  than  arsenic,  and  is  more  difficult  to  remove  from  the 
ore  by  heating. 

Nickel  behaves  much  like  copper  during  the  roasting  and 
fusion.  But  nickel  matte  is  heavier  than  copper  matte,  and 
when  a  sufficient  amount  is  present  it  may  be  separated  by  liqua- 
tion. See  nickel  smelting,  p.  273. 

Zinc  is  oxidized  during  the  roasting,  and  in  the  fusion  a  large 
portion  passes  into  the  slag  as  silicate,  often  causing  annoyance 
to  the  smelter  on  account  of  its  infusibility.  In  a  reducing 
atmosphere  some  of  the  zinc  is  reduced  and  volatilized.  It  is 
again  oxidized  upon  reaching  the  upper  part  of  the  furnace  and 
the  flues,  where  it  is  deposited. 

Lead,  if  present  in  any  considerable  quantity  in  the  ore,  will 


COPPER  SMELTING  199 

be  found  in  every  product  of  the  smeltery.  A  large  part  of  it 
is  reduced  in  the  matte,  and  most  of  this  is  subsequently  volatiliz- 
ed during  the  fusion  for  blister  copper.  A  smaller  portion  re- 
mains alloyed  with  the  copper.  It  should  be  understood  that 
lead  is  not  volatilized  like  zinc,  as  a  metal,  but  in  the  form  of 
oxide  and  sulphide. 

Silver  and  Gold  are  almost  entirely  retained  in  the  matte  if  it  is 
made  under  a  very  liquid  slag.  During  the  conversion  of  the  cop- 
per some  of  the  precious  metals  escape  with  the  slag,  and  in  the 
dust  of  the  converter,  but  the  larger  portion  remains  alloyed 
with  the  copper. 

EXTRACTION  OF  COPPER  IN  THE  WET  WAY 

The  so-called  wet  processes  look  to  the  conversion  of  the  cop- 
per in  the  ore  into  a  soluble  form.  It  is  subsequently  extracted 
with  water  and  precipitated  with  iron  or  by  means  of  the  elec- 
tric current.  The  fact  that  a  large  amount  of  copper-bearing 
material  can  be  treated  in  this  way  at  a  comparatively  low  cost 
makes  the  wet  methods  adaptable  to  low  grade  ores  and  products 
carrying  a  small  amount  of  copper. 

The  Sulphate  Process. — This  consists  in  converting  copper 
sulphide  into  sulphate  by  oxidation.  If  the  material  is  very  poor 
in  copper,  and  fuel  is  dear,  the  oxidation  may  be  brought  about 
In  a  slow  way  by  the  atmosphere.  The  ore  is  exposed  to  the 
weather  in  heaps  which  are  arranged  over  a  floor  of  clay  or  some 
material  that  will  not  soak  up  water.  Ditches  are  led  from  the 
piles  to  a  pond  in  which  the  drainage  is  collected.  As  the  oxida- 
tion proceeds  by  natural  processes,  the  rains  leach  out  the  ferric 
and  cupric  sulphates,  and  this  solution  is  caught  and  poured 
over  the  piles  repeatedly.  Finally  the  ore  is  leached  with  clear 
water,  and  the  combined  solution  is  evaporated  and  the  copper 
is  precipitated.  This  crude  method  is  not  of  importance  in  this 
country. 

The  more  usual  method  of  oxidizing  ores  is  by  roasting  them 
at  a  low  temperature.  With  proper  care  almost  the  entire  con- 
tent of  copper  in  the  ore  may  be  converted  into  sulphate  by 
roasting.  The  roasted  ore,  being  in  the  form  of  fines,  is  extract- 
ed in  suitable  tanks  or  vats. 


2OO  METALLURGY 

A  considerable  saving  may  result  from  the  recovery  of  drain- 
age water  from  ore  heaps  during  the  roasting.  If  the  heaps 
are  exposed  to  the  rains,  no  small  portion  of  the  sulphate  formed 
will  be  leached  out.  Waste  slags  from  smelteries  often  contain 
a  sufficient  amount  of  soluble  copper  to  pay  for  its  extraction. 

The  Chloride  Process. — The  copper  is  converted  into  the  chlo- 
ride by  treating  the  ore  with  a  solution  of  ferric  chloride — 

3CuS  +  2Fe2Cl6  =  2Fe2Cl4  +  Cu2Cl2  +  CuCl2  +  3S. 
Or,  more  commonly,  the  ore  is  first  roasted  to  drive  off  the  ex- 
cessive sulphur,  and  then  roasted  with  salt — 

CuS04  +  2NaCl  =  CuCl2  +  Na2SO4 
Cu20  -f  4NaCl  =  2CuCl2  -f  2Na2O. 

The  copper  is  precipitated  from  the  solution  of  the  chloride  as 

from  the  sulphate  solution. 


CHAPTER  XIX 


COPPER  REFINING 

As  has  been  already  stated,  the  properties  of  copper  are  in- 
iluenced  by  the  presence  of  very  small  amounts  of  impurities. 
The  purification  of  copper  for  the  market  must  therefore  be  most 
thorough.  It  is  said  that  in  this  country  a  rather  high  ideal 
exists  on  account  of  the  remarkable  quality  of  Lake  Superior 
copper.  No  doubt  the  phenomenal  growth  of  the  refinery  has 
been  largely  due  to  the  competition  between  the  copper  producers 
of  this  and  other  localities.  Two  distinct  processes  are  in  use 
for  the  purification  of  blister  copper — the  furnace  and  the  elec- 
trolytic processes. 

THE  FURNACE  PROCESS 

The  furnace  used  for  the  melting  and  refining  of  native  and 
blister  copper  is  a  large  reverberatory.  It  is  provided  with 
doors  for  charging  and  tapping,  and  a  large  grate  for  main- 
taining a  high  temperature.  Gas  furnaces  are  also  in  use.  The 
hearth  is  well  soaked  with  copper  by  melting  down  successively 
small  charges  which  have  been  spread  over  the  surface.  Pure 
metal  should  be  used  for  this  purpose,  since  it  stands  the  wear 
better,  and  besides,  impure  metal  would  be  the  means  of  con- 
taminating many  charges  after  they  had  been  refined. 

The  furnace,  having  been  made  ready,  is  charged  with 
blister  copper.  The  doors  are  closed  and  the  charge  is  melted 
down  under  a  reducing  flame.  The  thin  slag  which  forms  is 
skimmed  off,  and  the  furnace  doors  are  opened  to  expose  the 
surface  of  the  metal  to  the  air.  A  coating  of  cuprous  oxide  is 
iormed  at  once,  and  this  gives  rise  to  more  slag  by  its  fluxing 
action  on  the  impurities.  Such  action  is  hastened  by  skimming 
off  the  slag  at  intervals  of  an  hour.  The  escape  of  sulphur 
dioxide  has  the  beneficial  effect  of  agitating  the  bath,  thus  bring- 
ing the  oxidizing  medium  into  more  intimate  contact  with  the 
impurities.  After  the  bath  becomes  more  quiet  and  the  slag  is 


202  METALLURGY 

rich  in  cuprous  oxide  it  is  rabbled  continuously  for  a  period  of 
about  two  hours.  The  copper  now  becomes  "dry"  from  the 
absorption  of  cuprous  oxide,  and  a  test  shows  the  characteristic 
brick-red  color.  The  foreign  matter  has  been  removed,  and  it 
now  remains  only  to  reduce  this  oxide.  This  is  accomplished  by 
the  method  known  as  "polling."  A  long  pole  of  green  timber, 
as  large  as  can  be  managed,  is  thrust  into  the  bath.  The  hy- 
drocarbon gases  and  other  agents  reduce  the  copper,  the  sur- 
face of  the  bath  being  covered  with  fine  charcoal  to  prevent 
further  oxidation.  Tests  are  taken  and  submitted  to  mechanical 
treatment,  and  when  these  show  the  properties  of  pure  copper 
the  metal  is  tapped  and  cast  into  pig  molds  for  the  market.  The 
slag  is  returned  to  the  smelter. 

Elimination  of  Impurities. — Metals  of  low  melting  point  may 
be  separated  from  copper  by  heating  the  alloy  to  a  temperature 
insufficient  to  fuse  the  copper  but  considerably  above  the  fusion 
point  of  the  other  metal.1  The  older  process  for  separating  gold 
and  silver  was  to  melt  the  copper  with  lead,  the  bulk  of  the  lead 
separating  from  the  copper  by  liquation  and  carrying  with  it 
the  heavy  metals.  The  recovery  of  the  precious  metals  from 
the  lead  is  explained  under  the  metallurgy  of  lead.  The  ele- 
ments which  are  most  completely  removed  in  the  refinery  are 
sulphur,  iron,  silicon,  arsenic,  antimony,  bismuth  and  oxygen ; 
also  lead  and  zinc,  when  present  in  small  quantity.  Copper  of 
less  than  96  per  cent,  purity  is  treated  in  a  separate  furnace. 
Sometimes  a  small  quantity  of  white  metal  is  added  at  the  be- 
ginning of  the  operation  to  aid  in  the  elimination  of  arsenic  and 
antimony. 

The  impurities  are  oxidized  in  the  refinery,  and  are  either 
transferred  to  the  slag  or  volatilized.  The  copper  itself  acts  as 
a  carrier  of  the  oxygen.  This  is  shown  by  the  fact  that  a  much 
more  rapid  elimination  of  the  impurities  results  from  mixing 
cuprous  oxide  with  the  metal. 

The  oxygen  is  not  completely  removed  from  the  bath  by 
polling.  According  to  Egleston  it  can  not  be  reduced  to  o.i  per 

1  See  p.  224. 


COPPKR  REFINING  203 

cent.     About  4  to  6  per   cent,    of   the    total    charge    of   copper 
is  removed  in  the  slag  of  the  refinery. 

A  tilting  furnace,  operated  like  the  tilting  furnaces  of  the 
steel  maker,  has  been  recently  introduced  for  melting  copper  and 
matters.  With  such  a  furnace  there  is  a  great  saving  of  labor, 
since  both  the  slag  and  the  metal  are  discharged  mechanically. 

THE  ELECTROLYTIC  PROCESS 

The  fact  that  copper  can  be  precipitated  from  aqueous  solu- 
tions by  means  of  an  electric  current  has  been  known  for  more 
than  a  hundred  years,  though  it  had  but  few  practical  applica- 
tions until  after  Faraday's  discoveries  (1833).  Following  these 
were  the  inventions  of  electrotyping  and  electroplating.  The 
refining  of  copper  by  solution  and  precipitation  is  suggested  from 
the  fact  that  practically  pure  copper  may  be  precipitated  from 
solutions  containing  other  metals.  The  art  was  introduced  by 
Elkington,  and  his  first  commercial  refinery  was  built  at  Pem- 
bry,  Wales  in  1869.  It  is  interesting  to  compare  this  date  with 
that  of  the  advent  of  the  dynamo  (1867).  So  great  an  under- 
taking as  electric  refining  on  a  large  scale  could  never  have 
been  continued  had  not  the  dynamo  been  invented  and  the  cost 
of  the  electric  current  greatly  lessened.  The  demand  for  highly 
purified  copper  and  the  price  it  commands  have  more  than  justi- 
fied the  cost  of  refining  it  by  electrolysis.  Electrolytic  refining 
is  now  practiced  in  all  copper  producing  countries,  being  most 
adaptable  to  copper  containing  arsenic,  antimony,  bismuth  and 
the  precious  metals.  In  the  United  States  more  than  80  per 
cent,  of  the  entire  output  is  refined  in  this  way,  the  cost  having 
"been  reduced  to  four  or  five  dollars  a  ton.1 

General  Principles  of  Electrolysis. — In  the  drawing  (Fig  71) 
are  represented  two  copper  plates,  A  and  C,  immersed  in  a  dilute 
solution  of  sulphuric  acid.  To  the  heavy  plate,  A,  is  attached  a 
wire,  which  is  connected  with  the  positive  terminal  of  a  direct 
current  generator,  the  wire  from  C  is  connected  with  the  nega- 
tive terminal.  If  no  current  connection  were  made  the  copper 
of  both  plates  would  be  slowly  dissolved,  the  acid  being  decom- 
posed— 

1  Ulke,  "Modern  Electrolytic  Copper  Refining." 


2O4 


METALLURGY 


Cu  +  H2S04  =  CuS04  +  H,. 

But  copper  sulphate,  according  to  the  theory  of  Arrhenius,  is 
dissociated  in  an  aqueous  solution  into  copper  and  SO4  ions,  and 
the  current  in  passing  through  the  solution  gives  direction  to  these 
ions,  causing  copper  to  form  at  the  negative  and  SO4  at  the 
positive  plate — * 

CuS04  =  =  Cu  +  S04. 

The  positive  plate  is  thus  exposed  to  the  action  of  the  acid  radi- 
cal as  long  as  the  process  of  electrolysis  is  continued.  If  the 
SO4  is  not  immediately  combined  it  breaks  up  into  sulphur 
trioxide  and  oxygen.  Both  of  these  products  may  be  detected 
at  the  positive  plate.  The  chemical  action,  resulting  from  the 


Fig.  71. 

solution  of  the  copper  in  the  positive  plate,  largely  neutralizes 
the  back  pressure  that  is  set  up  as  the  current  passes  through 
the  solution.  For  this  reason  a  lower  pressure  is  needed  to 
drive  the  current  through  the  solution  than  would  be  required 
if  the  plate  were  insoluble  in  the  acid.  The  proportion  of  acid 
in  the  solution  gradually  diminishes,  while  the  copper  sulphate 
increases. 

In  the  application  of  the  principle  of  electrolysis  on  the  large 
scale  the  impure  copper  is  the  positive  plate,  and  the  pure  cop- 
per is  deposited  on  the  negative  plate.  The  positive  plate  is  call- 
ed the  anode,  and  the  negative  plate  is  the  cathode.  Collectively 
they  are  spoken  of  as  electrodes,  and  the  solution  is  the  elec- 
trolyte. The  amount  of  current  that  passes  through  the  elec- 
trolyte is  measured  in  units  called  amperes.  One  ampere  is  the 
1  Z.  phys.  Ch.,  1887,  1,  631. 


COPPER  REFINING  2O5 

amount  of  current  that  will  precipitate  1.18656  grams  of  copper 
in  an  hour.  The  electromotive  force,  or  pressure  under  which 
the  current  is  used  is  measured  in  volts,  and  the  unit  of  resist- 
ance that  is  offered  to  the  passage  of  the  current  is  the  ohm. 
in  conducting  the  process  of  electrolysis  on  the  commercial  scale 
a  number  of  electrodes  are  placed  in  each  vessel  holding  the 
solution,  and  they  are  arranged  close  together  to  minimize  the 
resistance.  Since  the  amount  of  copper  deposited  is  directly  pro- 
portional to  the  current  density  or  amperage,  as  much  current 
as  is  practicable  is  employed.  This  is  limited  by  the  increase  in 
the  cost,  of  generating  the  current  and  by  the  condition  of  the 
electrolyte.  Other  metals  in  solution  with  the  copper  may  like- 
wise be  deposited  on  the  cathode,  depending  upon  the  current 
strength  and  the  condition  of  the  electrolyte.  Practically,  about 
one  dunce  of  copper  is  deposited  in  24  hours  for  each  ampere  of 
current. 

The  Refining  Plant  and  Process. — The  refinery  consists  essen- 
tially of  the  power  house;  the  tank  house,  containing  the  tanks 
for  supporting  the  electrodes  in  the  solution,  also  the  appliances 
for  regenerating  the  electrolyte;  remelting  furnaces,  and  other 
equipment  for  working  up  the  products. 

The  tanks  for  holding  the  electrolytes  are  constructed  of  wood, 
and  lined  with  lead  or  other  acid-proof  material.  The  larger 
tanks  measure  10  feet  in  length,  3  feet  in  width  and  4^/2  feet 
in  depth.  Double  tanks  are  commonly  used,  the  two  being  sep- 
arated by  a  longitudinal  wall. 

The  anodes  are  of  cast  copper  from  the  smeltery.  They  are 
of  the  shape  shown  in  Fig.  72.  The  rectangular  dimensions  are 
about  30  inches  x  24  inches  and  the  thickness  ilA  inches.  The 
arms  at"  the  top  support  the  anode  in  the  tank.  The  cathodes 
are  of  electrolytic  copper,  rolled  down  to  7/32  inch  thickness 
and  cut  in  the  same  rectangular  dimensions  as  the  anodes.  The 
cathodes  are  supported  from  copper  rods  passing  through  loops, 
which  are  rivetted  on  in  the  manner  shown.  The  drawing  is 
a  section  through  a  double  tank  in  which  copper  is  refined. 

The  plan  of  a  double  tank  with  the  current  connections  is 
shown  in  Fig.  73.  The  heavy  lines  represent  the  anodes  and  the 


2O6 


METALLURGY 


narrow  lines  the  cathodes.     The  direction  of  the  current  is  in- 
dicated by  the  arrows. 

The  strength  of  current  employed  in  American  refineries  is  12 
to  15  amperes  per  square  foot  of  cathode  surface.  The  voltage 
is  increased  with  the  number  of  tanks  in  series.  As  there  is 


/?  NODE 


CATHODE 


Fig.  72. 

•clanger  of  loss  from  leakage  under  high  voltage  it  is  not  safe  to 
supply  "a  large  number  of  tanks  from  a  single  feed  wire.  The 
theoretical  pressure  of  1.16  volts  required  to  precipitate  copper 
from  the  sulphate  solution  is  reduced  in  practice  to  1/6-1/3 
volt,  by  virtue  of  the  soluble  anode.  The  electrodes  may  be- 


Fig.  73- 


come  short  circuited  in  one  of  two  ways.  The  growth  of  cop- 
per on  the  cathode  may  be  irregular,  accretions  of  crystals  ex- 
tending to  the  anode,  or,  the  deposit  of  "anode  mud"  on  the  bot- 
.tom  of .  the  tank  may  accumulate  more  rapidly  than  was  ex- 


COPPER  REFINING  207 

pccted,  and  touch  both  electrodes.  Frequent  inspection  is 
needed  to  remove  these  obstructions,  since  electrolytic  action 
ceases  as  soon  as  a  short  circuit  is  established. 

Under  normal  conditions  the  electrolyte  contains  about  19 
per  cent,  of  copper  sulphate,  6  per  cent,  of  sulphuric  acid  and 
75  per  cent,  of  water.  The  solution  is  frequently  tested  for 
free  acid  and  the  necessary  amount  is  restored.  The  circula- 
tion of  the  solution  keeps  its  composition  uniform,  but  the  im- 
purities and  the  excessive  amount  of  copper  sulphate  must  be 
removed  from  time  to  time. 

Purification  of  the  Electrolyte. — The  components  of  the 
anode  are  transferred  to  the  cathode;  dissolved  and  precipitated 
as  chemical  compounds;  dissolved  and  kept  in  solution,  or  left 
undissolved  altogether.  The  heavy,  undissolved  matter  falls  to 
the  bottom  of  the  tank,  forming  what  is  termed  anode  mud  or 
slime.  It  is  the  aim  to  keep  the  composition  of  the  solution 
and  the  strength  of  the  current  such  that  only  the  copper  will 
be  electrolyzed.  In  this  brief  outline  of  the  methods  of  treat- 
ing the  electrolyte,  the  history  of  the  several  impurities  of  the 
anode  may  be  followed. 

A  part  of  the  electrolyte  is  drawn  off  for  treatment.  The 
copper  sulphate,  which  is  all  the  time  increasing  in  the  solution 
is  removed  by  crystallization,  special  tanks  being  provided  for 
this  purpose.  Cuprous  oxide  and  cuprous  sulphide  go  into  the 
slime,  but  they  are  to  a  certain  extent  decomposed  and  added 
to  the  solution. 

Gold  and  Silver  fall  down  with  the  anode  mud. 

Iron,  Zinc,  Nickel  and  Cobalt  dissolve  and  remain  in  ttye 
solution. 

Bismuth  is  dissolved  and  partly  precipitated  as  the  sulphate. 

Arsenic  dissolves  and  precipitates  as  an  arsenite  as  the  solu- 
tion becomes  more  saturated.  If  the  bath  is  deficient  in  acid 
or  copper,  arsenic  will  be  added  to  the  cathode. 

Antimony  is  dissolved  and  partly  precipitated  as  a  basic  sul- 
phate. Like  arsenic  it  follows  the  copper  if  the  electrolyte 
becomes  neutral  or  low  in  copper. 


2O8  METALLURGY 

Lead  is  precipitated  as  the  sulphate,  most  of  which  settles  with 
the  slime. 

The  soluble  impurities  must  be  removed,  as  noted  above, 
since  pure  copper  can  not  be  precipitated  from  a  solution  which 
is  heavily  charged  with  other  metals.  A  portion  of  the  solu- 
tion is  therefore  under  treatment  all  the  time,  and  after  purifica- 
tion it  is  returned  to  the  circulation.  The  purification  of  the 
solution  is  quite  an  intricate  process  in  itself,  some  of  the 
methods  of  treatment  being  kept  secret.  The  iron,  nickel  and 
cobalt  may  be  removed  by  crystallization.  Arsenic,  antimony 
and  bismuth  are  precipitated  by  oxidizing  the  hot  solution  by 
means  of  fine  streams  of  air,  and  by  neutralizing  the  acid  with 
scrap  copper.  These  operations  are  carried  on  in  lead-lined 
vats  or  tanks. 

Treatment  of  the  Anode  Mud. — This  is  removed  from  the 
tanks  once  a  month,  or  as  often  as  necessary,  and  treated  for 
the  recovery  of  silver  and  gold.  It  is  first  boiled  with  sulphuric 
acid  to  dissolve  most  of  the  base  metals,  and  after  decanting  off 
the  acid  the  residue  is  washed  with  water.  The  residue  is  dried 
and  smelted  in  a  small  furnace  with  soda-ash  and  sand.  The 
silver  obtained  carries  both  copper  and  gold,  and  is  separated 
by  acid  parting  or  by  electrolysis.  (See  p.  270). 


CHAPTER  XX 


LEAD— ORES,  PROPERTIES,  ETC. 

History. — The  date  of  the  discovery  of  lead  is  not  known.  It 
was  employed  by  the  Egyptians,  Greeks  and  Romans  long  be- 
fore the  Christian  Era.  The  Romans  opened  mines  in  Britain, 
{Saxony  and  Spain,  some  of  which  are  still  operated.  Lead 
was  one  of  the  first  metals  mined  in  this  country,  though  it  is 
probable  that  in  the  treatment  of  lead  ores  by  early  American 
prospectors  silver  was  the  metal  sought.  Mines  were  operated 
before  the  Revolution  in  the  states  of  New  York,  Virginia  and 
North  Carolina,  and  in  the  Mississippi  Valley.  The  Rocky 
Mountain  deposits  came  into  prominence  in  1867,  and  the  lead 
industry  has  grown  rapidly  in  the  West  since  that  time.  The 
West  now  leads  in  the  production  of  lead. 

ORES 

Galena  (PbS). — This  is  by  far  the  most  important  ore  of 
lead.  It  occurs  both  crystalline  and  massive,  associated  with 
dolomite,  limestone  and  silicious  rocks.  Galena  is  not  in- 
frequently associated  with  pyrites  and  ores  of  zinc  and  silver. 
It  may  also  contain  arsenic,  antimony  and  other  impurities  in 
smaller  quantities. 

Cerusite  (PbCO3)  is  an  important  ore  in  the  West,  occurring 
but  sparingly  elsewhere.  It  is  usually  impure,  and  carries  other 
oxidized  forms  of  ore,  such  as  the  sulphate  and  oxide. 

Pyromorphite  (PbCl2+3Pb3P2O8)  is  met  with,  but  it  is  not 
an  important  ore. 

Lead  ores  occur  but  sparingly  in  the  Eastern  states,  though 
some  of  the  mines  in  the  Appalachian  region  are  still  productive. 
Next  to  those  of  the  Rocky  Mountains  the  Mississippi  Valley 
deposits  are  the  most  important.  Idaho,  Colorado,  Utah,  Mis- 
souri and  Kansas  are  the  leading  lead-producing  states. 

PROPERTIES 

Pure  lead  is  of  a  bluish-gray  color  and  highly  lustrous.     It 


J 


21 0  METALLURGY 

does  not  ordinarily  present  a  crystalline  structure  to  the  naked 
ey~,  but  under  proper  conditions  of  cooling  from  the  molten 
state  it  solidifies  in  octahedrons.  The  principal  properties  to 
which  lead  owes  its  usefulness,  are  its  malleability,  flow  and 
density.  Lead  melts  at  327°  C.,  and  boils  at  about  1,500°.  It 
alloys  readily  with  arsenic,  antimony  and  tin,  less  readily  with 
copper,  gold  and  silver,  and  with  zinc  it  is  said  to  form  no  true 
alloy. 

Effect  of  Impurities. — The  impurities  more  commonly  met 
with  in  commercial  lead  are  antimony,  arsenic,  bismuth,  copper, 
iron,  zinc  and  silver. 

Antimony. — This  metal  is  frequently  associated  with  lead 
ores.  If  a  large  proportion  is  present  the  ore  yields  an  alloy  of 
the  two  metals.  This  is  known  as  "hard  lead."  Besides  hard- 
,  eninj  lead  and  destroying  its  malleability,  antimony  has  the 
peculiar  property  of  causing  the  alloy  to  expand  when  cooled 
from  the  molten  state. 

Arsenic  is  also  frequently  associated  with  lead  ores  and  its 
effect  upon  the  properties  of  lead  is  similar  to  that  of  antimony, 
rendering  it  hard  and  brittle. 

Bismuth  is  much  less  frequently  met  with  and  is  not  often 
present  in  sufficient  quantity  to  injure  lead.  It  lowers  the 
melting  point,  and  renders  the  lead  hard  and  crystalline. 

Copper  is  a  very  common  impurity  in  unrefined  lead,  and  is 
often  added  in  the  manufacture  of  certain  alloys.  The  small 
amount  that  is  left  in  refined  lead  is  not  sufficient  to  interfere 
with  its  working  properties. 

Silver  in  small  quantities  is  a  very  common  ingredient  of  lead 
ores,  and  is  therefore  to  be  expected  in  the  lead  as  it  comes  from 
the  smelter.  Silver-lead  alloys  that  are  purposely  made 
in  the  extraction  of  silver  are  known  as  "work  lead."  Small 
percentages  of  silver  lower  the  melting  point  of  lead,  and  large 
quantities  harden  it  and  raise  the  melting  point. 

Iron  alloys  with  lead  only  under  special  conditions,  and  is 
never  an  interfering  element.  Commercial  lead  contains  but 
a  few  hundredths  of  a  per  cent,  of  iron. 


LEAD  211 

Zinc  is  not  a  common  impurity  in  lead.  It  imparts  a  lighter 
color  and  renders  lead  hard  and  brittle. 

Chemical  Properties. — The  chemical  properties  of  special  in- 
terest in  the  metallurgy  of  lead  are  its  action  toward  oxygen 
and  sulphur,  its  basic  character,  and  the  ease  with  which  it  is 
reduced  from  all  its  compounds.  When  exposed  to  moist  air, 
or  when  heated  in  air  just  above  the  fusion  point  lead  becomes 
coated  with  a  dull-gray  film  of  suboxide  (Pb2O).  At  a  higher 
temperature  litharge  (PbO)  is  formed,  and  at  a  still  higher 
temperature  litharge  is  further  oxidized  to  red  lead  (Pb3OJ. 
The  most  important  of  these  oxides  in  metallurgy  is  litharge. 
This  melts  at  a  red  heat  and  is  very  volatile  at  higher  tempera- 
tures. It  is  strongly  basic,  forming  an  easily  fusible  slag  with 
silica.  The  oxides  of  lead  are  reducible  with  carbon. 

Lead  combines  with  sulphur  at  a  moderately  high  tempera- 
ture, forming  a  lustrous,  brittle,  gray  mass  (PbS).  Tjhis  is 
also  volatile  at  furnace  temperatures,  and  is  less  fusible  than 
lead.  Heated  in  the  air  lead  sulphide  is  converted  into  the 
oxide  and  sulphate.  If  either  the  sulphide  or  the  sulphate  is 
fused  with  the  oxide,  decomposition  of  both  compounds  takes 
place  with  the  liberation  of  sulphur  dioxide  and  lead.  Roasted 
galena  contains  all  three  of  these  compounds.  The  sulphide  of 
lead  is  also  decomposed  when  heated  with  some  metals,  notably 
iron,  and  with  strong  basic  oxides  such  as  lime.  Lead  com- 
pounds in  general  are  decomposed  by  fusion  with  strong  bases. 
The  sulphate  is  soluble  in  alkaline  acetate  solutions,  and  from 
these  lead  may  be  precipitated  by  electrolysis. 

Lead  is  not  readily  acted  on  by  either  sulphuric  or  hydro- 
chloric acid,  but  it  is  freely  dissolved  by  nitric  acid. 

PREPARATION  OF  LEAD  ORES  FOR  SMELTING 

The  oxidized  ores  are  easily  reduced  with  carbonaceous  fuel 
and  require  no  special  treatment  beforehand,  other  than  some 
separation  from  the  gangue.  Galena,  to  which  attention  is  here 
directed,  may  be  further  concentrated  with  great  advantage  by 
roasting.  The  ores  of  lead  are  extremely  variable  in  composi- 
tion, and  their  treatment  for  the  recovery  of  lead  and  other 
metals  presents  one  of  the  most  complicated  propositions  in 


212  METALLURGY 

metallurgy.  The  first  operation  is  to  separate,  as  far  as  pos- 
sible, the  lead-bearing  mineral  from  the  vein  stuff  or  from 
other  associated  ores.  Copper  and  iron  pyrites  and  zinc  blende 
are  often  present.  A  good  deal  of  concentrating  may  be  done 
at  the  mine  by  hand  picking.  Further  concentration  is  af- 
fected by  washing,  the  jig  being  specially  adaptable  to  washing 
lead  ores.  A  process  employing  magnetic  machines  for  concen- 
trating pyritous  ores  of  zinc  and  lead  is  outlined  on  p.  233. 

Roasting. — There  are  but  few  instances  in  which  lead  ores 
are  not  roasted  before  smelting.  The  roasting  process  is,  how- 
ever, often  inseparable  from  that  of  smelting,  both  being  per- 
formed in  the  same  furnace. 

If  the  ore  is  rich  in  sulphur  and  in  lump  form  it  may  be 
roasted  in  heaps  or  stalls,  but  open  air  roasting  is  rarely,  if  ever, 
resorted  to  in  this  country.  The  ore  is  usually  fine,  crushed 
if  necessary,  and  is  roasted  in  some  form  of  reverberatory 
furnace.  The  hand  reverberatory,  described  on  p.  176,  is  the 
most  common.  Mechanical  roasters,  and  in  a  few  instances, 
shaft  furnaces  are  employed. 

The  roaster  is  often  heated  by  means  of  waste  heat  from  the 
smelting  furnace,  the  two  furnaces  being  under  the  same  roof, 
and  the  hearth  of  the  smelting  furnace  being  situated  on  a  lower 
level  than,  and  close  to  that  of  the  roaster.  With  such  an  ar- 
rangement there  is  a  considerable  saving  in  the  handling  of  the 
ore.  In  connection  with  the  roaster,,  chambers  or  flues  are 
built  for  settling  the  fume.  The  subject  of  lead  fume  will  be 
dealt  with  in  the  next  chapter. 

The  Process. — The  ore  is.  charged  through  a  hopper  in  the 
roof  of  the  furnace  and  leveled  down  over  the  hearth.  It  is 
charged  at  the  cooler  end  of  the  hearth  and  during  the  roasting 
it  is  turned  and  moved  toward  the  fire-bridge.  The  furnace 
temperature  is  regulated  and  the  ore  is  frequently  stirred  to 
prevent  fusion.  It  is  readily  seen  how  fusion  or  caking  would 
check  oxidation.  The  temperature  employed  and  the  extent  of 
the  roasting  depend  upon  the  nature  of  the  ore  and  the  way 
in  which  it  is  to  be  smelted.  As  a  rule,  the  ore  is  allowed  to 
sinter  but  slightly  on  the  finishing  hearth.  As  it  is  withdrawn 


LEAD  21$ 

the  roasted  ore  contains  lead  sulphate,  oxide  and  unaltered  sul- 
phide, with  possibly  some  metallic  lead.  The  analyses  below 
show  the  composition  of  an  ore  before  and  after  roasting.1 

Pb  Fe  Zn  SiO2  S  SO3  O 

Raw  Ore 47.29        20.36        0.67        0.49        29.86          ...  

Sintered  Ore 54.27        24.06        0.87        0.80          2.72         2.25         13.41: 


Hofman's  "Metallurgy  of  Lead,"  p.  167. 


CHAPTER  XXI 


LEAD  SMELTING 

Lead  is  at  once  a  very  easy  metal  to  reduce  from  its  ores 
and  one  of  the  most  difficult  to  recover  completely.  Unless 
properly  guarded  against,  serious  losses  will  result  from  vola- 
tilization and  the  tendency  of  lead  compounds  to  enter  the  slags. 
The  subject  being  a  very  complex  one,  only  typical  processes 
will  be  described  in  this  text.  The  subject  will  be  studied  un- 
der three  heads,  according  to  the  types  of  furnaces  employed. 

REVERBERATORY  SMELTING 

Though  not  so  much  used  in  America,  reverberatory  furnaces 
are  favored  among  foreign  smelters.  They  belong  to  older  prac- 
tice, but  in  many  cases  they  are  undoubtedly  more  adaptable  to 
the  localities  in  which  they  are  used  than  any  other  furnace. 
They  are  cheaper  to  construct  and  make  purer  lead  than  is  made 
in  blast  furnaces,  but  their  output  is  smaller  and  they  are  not  so 
well  suited  for  ores  of  low  or  irregular  grades. 

As  a  representative  of  this  style  the  English  reverberatory  may 
be  taken.  The  main  differences  in  the  construction  of  this 
and  other  reverberatory  furnaces,  designed  for  smelting  pur- 
poses, may  be  understood  from  the  hearth  plan  (Fig.  74). 
The  fire-box  is  shown  at  the  right  of  the  drawing  and  the  flue 
entrances  to  the  stack  at  the  left.  Thei  furnace  has  three 
working  doors  on  both  sides  and  a  charging  hole  in  the  roof. 
It  is  built  of  common  brick  and  lined  throughout  with  fire- 
brick. The  walls  are  held  together  with  buckstaves  and  tie- 
rods.  The  bottom  is  built  up  with  fire-brick,  giving  the  proper 
slope  from  both  ends  and  the  back  toward  the  front  of  the  fur- 
nace. Upon  the  brick  work  is  laid  a  deep  lining  of  sand  and 
slag  from  previous  operations.  The  hearth  slopes  toward  the 
middle  door  on  the  front  side  of  the  furnace,  and  in  the  low- 
est part  there  is  a  sump  or  well  in  which  the  lead  accumulates. 
A  tap-hole  is  provided  for  drawing  off  the  lead  from  the 
well,  and  an  iron  pot  is  placed  outside  to  receive  it. 


LEAD  SMELTING 


215 


The  Process. — About  one  ton  of  fine  ore  is  charged  and  spread 
over  the  hearth.  The  ore  begins  to  decrepitate  at  once  since 
the  furnace  is  preheated.  The  temperature  of  the  furnace  is 
kept  low  at  first  and  the  atmosphere  strongly  oxidizing. 
Should  any  ore  begin  to  fuse  it  is  raked  away  to 
a  cooler  part  of  the  hearth.  The  ore  is  turned  and  stirred  on 
the  hearth  to  facilitate  even  and  complete  roasting.  The  roast- 
ing requires  about  two  hours,  at  the  end  of  which  time  the 
doors  are  closed  and  the  fire  is  urged,  to  bring  on  the  melting 
stage.  A  quantity  of  lead  now  runs  from  the  ore  and  collects 
in  the  well  from  which  it  is  tapped  into  the  pot  outside.  Some 
undecomposed  galena  also  melts  and  forms  a  layer  on  top  of 
the  lead.  This  is  "set  up"  by  mixing  it  with  lime,  and  the  now 
stiffened  mass  is  raked  back  on  the  upper  part  of  the  hearth 


Fig.  74- 

with  the  ore.  This  is  followed  by  another  roasting  and  fusing, 
which  results  in  the  liberation  of  most  of  the  remaining  lead. 
If  a  large  amount  of  galena  still  remains  more  lime  is  added, 
and  the  roasting  and  fusing  are  repeated.  The  lead  is  pro- 
tected by  a  covering  of  slack  while  in  the  well.  After  tap- 
ping into  the  pot  it  is  ladled  and  cast  into  molds.  The  slag 
contains  too  much  lead  to  be  rejected,  and  is  smelted  in  a 
separate  furnace.  This  process  is  only  suitable  for  smelting 
rich  sulphides.  It  belongs  to  those  known  as  the  "air  reduc- 


2l6  METALLURGY 

tion"  or  "reaction"  processes,  in  which  no  reducing  agent  is 
added,  the  lead  being  liberated  by  the  double  decomposition 
of  its  own  compounds. 

With  silicious  ores  the  treatment  is  different.  Formerly  the 
roasted  ore  was  fused  with  scrap  iron  in  a  reverberatory  fur- 
nace (Cornish  process).  The  ore  is  first  roasted  somewhat 
as  above  described,  until  the  residue  yields  no  more  lead.  The 
residue  is  then  mixed  with  coal,  spread  over  the  furnace  hearth 
and  the  iron  is  added.  The  temperature  is  then  raised  very 
high,  the  air  being  excluded.  The  lead  and  a  small  amount  of 
unaltered  sulphide  run  out,  leaving  a  slag  which  is  almost  free 
from  lead.  This  process  has  been  practically  abandoned  in 
favor  of  hearths  and  blast  furnaces. 

HEARTH  SMELTING 

The  ore  hearth  in  lead  smelting  may  be  considered  as  inter- 
mediate between  the  reverberatory  and  the  blast*  furnace.  The 
style  of  hearth  used  in  England,  better  known  as  the  Scotch 
hearth,  is  described  by  Percy.1  In  this  the  or£  is  roasted  and 
fused  simultaneously,  but  the  furnace  can  not  be  operated  con- 
tinuously on  account  of  overheating.  The  hearths  used  in  this 
country  work  on  the  same  principle  except  that  the  process  is 
not  interrupted,  the  hotter  portions  of  the  furnace  being  water- 
cooled. 

The  hearth  consists  essentially  of  a  rectangular,  cast  iron  box. 
set  in  masonry,  and  above  this  a  rectangular  enclosure  formed 
by  water-cooled  blocks  of  cast  iron,  with  one  of  the  longer 
sides  left  open.  This  is  the  front  side  of  the  hearth  from 
which  the  lead  flows  over  an  inclined  plate  when  the  box  or 
well  is  full.  The  blast  is  supplied  from  three  tuyeres  pass- 
ing through  the  back  wall.  A  hood  communicating  with  a  stack 
is  placed  directly  over  the  hearth  for  carrying  away  the  fumes. 

The  Process. — A  new  hearth  is  heated  for  some  time  with  a 
good  fire  before  any  ore  is  charged.  The  first  charges  are  light 
and  consist  largely  of  silicious  slag.  The  ore,  mixed  with  lime, 
is  increased  to  the  normal  charge  and  is  covered  with  a  layer 
of  fuel.  The  blast  in  playing  upon  the  burning  fuel  brings  the 
1  Metallurgy  of  Lead,  pp.  278-289. 


LEAD   SMELTING 

entire  mass  to  a  glowing  heat.  The  lead  is  rapidly  reduced  and 
trickles  down  into  the  basin  and  overflows  through  the  spout. 
The  slag  accumulates  on  the  ash  bed  until  it  is  tapped. 

The  hearth  is  well  suited  for  smelting  coarsely  crushed  ores. 
The  lead  made  by  this  process  may  be  of  a  high  degree  of 
purity,  but  the  slags  are  not  clean.  They  are  usually  smelted 
in  a  specially  constructed  blast  furnace. 

BLAST  FURNACE  SMELTING 

Blast  furnaces  have  practically  superseded  all  others  in  this 
country  for  smelting  lead  ores.  They  have  been  found  to  be 
the  most  suitable,  largely  on  account  of  the  non-uniformity  of 
the  ores  that  have  to  be  treated  at  the  same  smeltery.  The  blast 
furnace  is  of  German  origin,  though  it  has  undergone  many 
changes  since  it  was  introduced  into  this  country. 

Fig.  75  represents  a  modern,  American  furnace  for  smelting 
lead  ores.  This  furnace  is  rectangular  in  cross-section,  and  in 
some  respects  it  resembles  the  rectangular  copper  cupola.  The 
bosh  walls  are  water-jacketed,  and  the  upper  walls  are  built  of 
common  brick  with  a  lining  of  fire-brick.  These  walls  are  very 
thick  especially  toward  the  base,  and  are  supported  on  cast  iron 
columns.  In  this  style  of  furnace  the  shaft  terminates  at  the 
level  of  the  charging  floor,  the  top  being  covered  with  cast 
iron  or  steel  plates.  The  fumes  and  products  of  combustion  are 
led  downward  through  a  steel  pipe  to  dust  chambers.  The  en- 
trance to  the  downtake  is  below  the  level  of  the  charging  floor 
as  shown  by  the  circular  outline. 

The  crucible  .of  the  furnace  is  lined  with  fire-brick.  Since 
these  are  penetrable  by  molten  lead,  a  bottom  plate  is  placed 
directly  under  the  hearth  to  prevent  wasting  of  the  lead.  The 
lead  runs  from  the  furnace  automatically  through  a  siphon  tap 
from  which  it  flows  into  an  outside  retainer.  Above  the  level 
of  the  lead  in  the  furnace  there  is  a  tap-hole  for  the  slag. 

The  Process. — The  furnace  is  carefully  heated  with  a  wood 
lire  followed  by  coke  and  light  charges  of  slag.  The  blast  is 
turned  on  and  increased  as  required.  Ore  is  introduced  and  the 
amount  is  gradually  increased  to  the  normal  charges.  The  slag- 
is  carefully  watched,  this  being  the  best  indicator  of  the  con- 
dition of  the  furnace. 


218 


METALLURGY 


The  furnace  having  been  started,  the  regular  charging  is  con- 
tinued. The  materials  are  loaded  in  barrows,  weighed  and 
charged  by  hand.  Materials  classed  as  ores  consist  of  raw  and 
roasted  ores  and  slags.  The  fuel  is  generally  coke,  though 
charcoal  and  wood  are  used  in  some  places.  Iron  and  iron 
oxide  are  added  as  reducing  and  fluxing  agents.  Lime  is  add- 
ed as  a  flux  and  a  desulphurizer.  In  regular  working  the 


Level  of  Charging  Floor 


75- 


analysis  of  the  materials  is  made  the  basis  for  calculating  the 
charges.  The  condition  of  the  slag  is  the  constant  means  of 
knowing  how  the  furnace  is  working.  The  smelter  is  warned 
by  its  appearance,  as  it  runs  from  the  furnace  and  cools,  of 
trouble  which  he  may  avert  by  altering  the  blast  or  the  burden. 
Experience  has  taught  him  to  estimate  roughly  the  composition 
of  a  slag  and  to  ascertain  the  presence  of  abnormal  ingredients 
in  it,  from  the  physical  state.  The  example  below  is  of  a  typical 
blast  furnace  charge.1 

1  Hofman's  "Metallurgy  of  Lead,"  p.  215. 


LEAD  SMELTING 


219 


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.220  METALLURGY 

Most  of  the  lead  in  the  blast  furnace  burden  is  completely 
reduced.  It  accumulates  in  the  crucible  of  the  furnace  until 
-of  sufficient  height  to  flow  through  the  channel  into  the  well. 
Some  molten  lead  is  left  in  the  furnace  all  the  time  as  a  safe- 
guard against  "freezing."  The  lead  is  ladled  and  cast  into 
pig  molds,  automatic  devices  being  used  at  some  works.  It  is 
known  as  base  bullion  and  is  to  be  refined. 

Along  with  the  lead  are  melted  the  matte  and  slag,  and  some- 
times a  speiss.  The  lead  separates  almost  completely  from  the 
other  fused  substances,  but  there  is  never  a  perfect  separation 
of  matte  and  slag  in  the  furnace.  The  non-metallic  substances 
.are  therefore  tapped  together  into  a  ladle  in  which  they  are  given 
time  to  separate.  The  ladle  has  the  form  of  a  paraboloid,  and 
is  carried  on  a  two-wheel  truck.  It  is  provided  with  a  tap-hole 
a  few  inches  above  the  bottom.  The  mixture  of  matte  and  slag 
is  allowed  to  stand  until  the  matte  settles  to  the  bottom.  The 
tap-hole  is  then  opened  to  draw  off  the  slag.  Another  method 
-of  handling  the  melt  is  to  allow  the  slag  to  overflow  the  pot  or 
iadle. 

The  gases  passing  from  the  top  of  the  furnace  carry  with 
them  small  particles  of  ore  and  coke  together  with  a  quantity 
•of  lead  fume.  The  coarse  particles  are  detained  in  chambers 
situated  near  the  furnace,  and  the  fume  is  deposited  and  re- 
covered by  one  of  the  methods  described  at  the  end  of  this 
•chapter.  According  to  Hofman  an  average  of  5  per  cent,  of 
the  weight  of  ore  charged  is  carried  over  as  flue  dust. 

Chemistry  of  Lead  Smelting. — The  principal  chemical  changes 
occurring  during  the  smelting  of  lead  ores  .may  be  expressed 
in  the  following  equations : 

PbS  +  2PbO  =  =  Ph,  +  SO2 
PbS  -f  PbS04  ==  Pb2  +  2S02 
PbS  +  2PbS04  =  =  Pb  -f  2PbO  +  3SO2 

PbS  -f  Fe  =  Pb  +  FeS 
4PbS  -f-  4CaO  =  Pb4  +  3CaS  +  CaSO4 

2PbO  +  C  ==  Pb,  +  C02 

2PbO.SiO2  +  Fe2  ==  Pb2  +  2FeO.SiO2 

2PbO.SiO2  +  2Fe2O3  +  6CO  =  Pb2+2FeO.SiO2+6CO2H-  Fe2. 


LEAD   SMELTING  221 

The  first  three  equations  represent  the  principal  chemical 
changes  in  the  air  reduction  process.  The  others  belong  more 
particularly  to  the  blast  furnace  process.  The  relation  of  the 
more  important  substances  in  lead  smelting  may  be  studied 
separately  with  advantage. 

Iron  and  Manganese  Oxides  act  as  oxidizers  and  as  fluxes 
with  the  silicious  gangue  of  the  ore.  Some  of  the  iron  is  re- 
duced by  carbon  and  carbonic  oxide,  in  which  state  it  is  a  power- 
ful reducer  with  the  compounds  of  lead.  There  is  an  advantage 
in  using  iron  ore  in  the  blast  furnace  rather  than  metallic  iron, 
because  the  ore  mixes  more  intimately  with  the  charge. 

Lime  and  Magnesia  act  as  desulphurizers  and  basic  fluxes. 
If  lime  vwere  not  added  to  high  silica  charges  the  iron  oxide 
would  be  drawn  upon  so  heavily  as  to  lessen  the  available 
metallic  iron  for  reduction.  Limestone  is  usually  cheaper  than 
the  high  grade  iron  ore  which  the  smelter  uses.  Some  lime  is 
\ery  desirable  in  blast  furnace  slags,  as  it  favors  the  separation 
of  the  matte,  but  an  excessive  amount  raises  the  fusion  point 
and  renders  the  slag  too  stiff. 

Zinc  Blende  is  a  most  troublesome  substance  to  lead  smelters, 
in  the  roasted  ore  it  is  largely  converted  into  the  oxide.  It  is 
also  oxidized  in  the  blast  furnace,  chiefly  by  iron  and  manganese 
oxides.  The  zinc  oxide  enters  the  slag  rendering  it  stiff  and 
very  difficult  to  fuse.  Crusts  or  accretions  may  result  from 
the  presence  of  zinc,  causing  a  choking  of  the  blast  and  re- 
tarding the  descent  of  the  charge.  Some  zinc  is  reduced  in  the 
lower  part  of  the  blast  furnace  and  volatilized.  This  is  oxidized 
and  deposited  in  the  upper  part  of  the  furnace  and  in  the  dust 
chambers. 

Arsenic  is  partly  volatilized  and  partly  reduced  and  alloyed 
with  the  lead.  A  still  larger  portion  is  alloyed  or  combined 
with  iron  in  a  speiss.  The  speiss  is  rather  difficult  to  fuse,  and 
may  form  accretions  in  the  lower  part  of  the  furnace.  It  re- 
tards the  separation  of  lead  from  the  matte. 

Antimony  is,  for  the  most  part,  reduced  and  alloyed  with  the 
lead.  If  the  charge  is  poor  in  iron  a  larger  amount  is  volatilized 
than  under  normal  conditions  in  the  blast  furnace. 


222  METALLURGY 

Fluor-spar  is  sometimes  of  use  in  rendering  slags  more  liquid, 
It  may  be  added  with  advantage  to  charges  containing  zinc  or 
too  much  lime. 

The  following  analyses  of  slags,  taken  from  Hofman's  "Metal- 
lurgy of  Lead"  may  be  taken  as  representing  good  practice. 

SiO2  FeO  and  MnO        CaO,  BaO,  MgO 

Kilers 28  50  12 

"      30  40  20 

lies •     32  33  23 

Schneider 33  33  24 

Hahn 34  5°  I2 

"       36  40  20 

Murry 40  34  26 

Lead  Fume. — With  any  furnace  in  which  a  quantity  of  lead- 
bearing  material  is  treated,  some  appliance  is  needed  for  re- 
covering the  fume.  The  method  for  recovering  fume  depends 
upon  its  composition,  quantity,  temperature,  etc.  The  only 
method  in  common  use  until  recently  was  to  conduct  the  fur- 
nace gases  through  long  horizontal  flues,  the  gases  being  cooled 
in  this  way  and  the  velocity  checked  until  the  solid  matter  was 
deposited.  Some  of  the  flues  at  the  'older,  English  smelteries 
were  more  than  two  miles  in  length.  Those  of  the  present  time 
are  much  shorter,  the  settling  of  the  fume  being  effected  in  a 
different  way.  Metal  has  been  largely  substituted  for  brick  in 
the  construction  of  the  flues,  and  some  water-cooled  flues  are 
in  use  for  quickly  cooling  the  gases.  The  velocity  may  be 
checked  in  a  shorter  distance  by  enlarging  the  flue  at  intervals 
or  by  partitioning  it  into  chambers  so  that  the  gases  must  pass 
from  one  to  the  other. 

The  method  of  condensing  fume  by  forcing  it  through  water 
or  by  spraying  it  with  water  has  had  but  little  application  on 
account  of  the  difficulties  in  the  management  and  the  cost  of 
the  apparatus. 

The  method  of  filtering  through  cloth,  better  known  as  the 
Lewis  and  Bartlett  process  has  been  in  use  many  years  for 
collecting  lead  and  zinc  oxides  in  the  manufacture  of  paint  pig- 
ments. A  description  of  the  process  and  its  application  in  hearth 
smelting  is  given  by  F.  P.  Dewey1.  This  process  is  now  suc- 
1  Trans.  Amer.  Inst.  Min.  Eng.,  18,  674. 


LEAD  SMELTING  223 

cessfully  used  in  connection  with  blast  furnaces.  It  consists 
in  forcing  the  cooled,  fume-ladened  gases  through  muslin  or 
wooden  bags,  some  30  feet  in  length,  and  18  inches  in  diameter. 
The  large  volume  of  gases  from  a  blast  furnace  plant  is  neces- 
sarily distributed  to  a  great  number  of  these  bags.  The  bags 
.are  distended  by  the  pressure  from  within,  and  the  gases  pass 
freely  through  the  meshes  of  the  cloth,  but  the  fume  is  retain- 
ed. The  attempt  has  been  made  to  use  bag  niters  for  recover- 
ing the  fume  from  lead  roasters,  but  so  far  none  have  been 
made  to  withstand  the  action  of  the  acid  vapors.  It  has  been 
found  that  cloth  which  is  dyed  with  titanium  chloride  lasts 
for  a  much  longer  time. 

The  fume  is  returned  to  the  smelter.  If  it  is  to  be  used  in 
the  blast  furnace  it  must  be  caked  or  briquetted.  Oxidized 
dust  may  be  made  into  bricks  after  mixing  it  with  some  binding 
agent.  Blast  furnace  dust,  containing  so  much  lead  sulphide,  is 
inflammable  and  is  burnt  after  it  has  been  shaken  from  the  bags. 
This  converts  it  into  a  cake  of  lead  oxide  and  sulphate. 


CHAPTER  XXII 


LEAD  REFINING 

Lead  for  the  market  must  be  practically  pure.  Aside  from 
the  worthless  impurities  it  may  contain  valuable  metals  such  as 
antimony  and  the  precious  metals.  The  refining  may  therefore 
be  not  only  a  necessity  but  also  a  clear  gain.  The  separation 
of  the  base  impurities  from  lead  is  commonly  termed  softening. 
It  precedes  the  process  of  desilverizing. 

SOFTENING 

This  process  consists  in  melting  a  large  quantity  of  lead  in 
a  reverberatory  furnace,  and  exposing  it  to  an  oxidizing  atmos- 
phere until  the  impurities  separate  in  a  dross  or  by  volatilization. 
The  lead  is  sometimes  melted  outside  and  poured  into  the  fur- 
nace, but  it  is  usually  charged  cold.  It  is  melted  down  slowly 
to  facilitate  oxidation  and  the  separation  of  metals  of  a  higher 
melting  point  than  lead.  The  dross  which  forms  at  first  is  dark 
in  color  and  contains  much  of  the  copper,  arsenic,  sulphur  and, 
in  general,  those  substances  which  do  not  alloy  readily  with 
lead  and  which  oxidize  most  easily.  The  dross  is  skimmed  off 
from  time  to  time  so  that  a  fresh  surface  will  be  exposed  and 
a  clean  scum  of  lead  oxide  formed.  After  the  first  skimming 
the  temperature  is  raised  to  a  fulL  red  heat,  and  if  the  dross 
fuses,  lime  is  added.  The  process  is  sometimes  shortened  by 
adding  litharge.  Oxidation  is  further  hastened,  by  stirring  the 
bath.  Very  efficient  stirring  is  effected  by  blowing  dry  steam 
from  a  jet  held  under  the  surface  of  the  lead,  but  the  practice 
is  unusual. 

Antimony,  if  present  in  considerable  amount,  is  removed  by 
cooling  the  bath  until  a  crust  of  antimoniate  of  lead  forms. 
The  crust  is  removed  and  the  operation  is  repeated. 

Lead  that  is  rich  in  copper  is<  liquated  before  further  treat- 
ment. The  pigs  of  copper-lead  are  placed  in  a  reverberatory 
furnace  with  a  sloping  hearth,  the  lower  part  being  toward  the 


LEAD  REFINING  225 

fire-bridge.  The  lead  is  first  subjected  to  a  temperature  that  is 
below  its  melting  point,  and  is  then  moved  down  gradually  in- 
to the  hotter  part  of  the  furnace.  The  lead  melts  and  runs 
away,  leaving  an  impure,  coppery  residue.  This  method  of 
separating  metals  of  different  melting  points  is  called  "sweating." 

DESILVERIZING 
i .     By  the  Pattinson  Process 

Pattinson  introduced  his  process  for  concentrating  silver  in 
lead  in  1833.  Before  that  time  lead  containing  very  small 
amounts  of  silver  was  not  desilverized.  The  only  method  then 
known  for  separating  the  two  metals  was  by  cupellation,  and 
this  was  too  expensive  for  poor  alloys.  Pattinson's  process  is 
analogous  to  the  well  known  methods  of  purification  by  crys- 
tallization in  the  manufacture  of  pure  chemical  salts.  Jt  de- 
pends upon  the  fact  that  alloys  of  lead  containing  less  than  650 
ounces  of  silver  per  ton  (1.8  per  cent.)  melt  at  a  lower  tem- 
perature than  pure  lead  does,  in  consequence  of  which  the  purer 
lead  solidifies  first  when  a  molten  mass  of  the  alloy  cools. 

The  original  process  as  described  by  Pattinson,  is  given  in 
Percy's  "Metallurgy  of  Lead."  The  desilverizing  plant  consists 
of  eight  or  more  hemispherical,  iron  kettles,  supported  over  in- 
dependent fire-places.  A  truck,  running  on  an  overhead  rail- 
way, or  a  crane  is  provided  for  supporting  the  ladle  and  moving 
it  from  one  kettle  to  another.  The  ladle  is  for  lifting  out  the 
lead  crystals,  the  bottom  being  perforated  to  allow  the  liquid 
metal  to  run  back. 

In  starting  the  operation  six  or  more  tons  of  base  bullion  are 
charged  into  the  middle  kettle.  The  kettle  is  heated  until  the 
lead  is  melted  and  covered  with  a  scum  of  dross.  The  fire  is 
then  drawn  and  the  dross  is  skimmed  off.  Cooling  is  hastened 
by  sprinkling  water  over  the  surface  of  the  metal,  and  any  crusts 
that  form  are  broken  and  pushed  down  to  melt  again.  As  the 
melting  point  of  pure  lead  is  reached  the  crystals  of  lead  begin 
to  form,  and  the  cooling  is  allowed  to  proceed  slowly.  The 
crystals  are  skimmed  off  with  the  perforated  ladle,  and  after 
draining,  they  are  transferred  to  the  next  kettle  which  is 


226 

already  hot  enough  to  melt  them.  The  skimming  is  continued 
as  the  crystals  form  until  the  silver  has  been  concentrated  suf- 
ficiently, when  the  enriched  alloy  is  removed  to  the  next  kettle 
on  the  left,  the  lead  crystals  being  moved  to  the  right.  The 
kettle  thus  emptied  is  charged  with  new  lead  and  the  operation 
is  repeated,  while  the  concentration  is  conducted  in  the  same 
manner  in  the  other  kettles,  the  lead  becoming  purer  with  each 
crystallization  and  the  alloy  being  enriched  in  silver  at  the  same 
time.  As  the  successive  portions  of  the  original  charge  become 
smaller,  full  charges  for  the  kettles  may  be  made  up  by  combin- 
ing any  portions  of  the  same  tenor  in  silver,  or  portions  from 
another  lot  of  bullion.  The  purified  lead,  which  contains  but  j£ 
ounce  of  silver  per  ton  goes  to  the  market,  and  the  enriched  bul- 
lion is  cupelled  or  further  concentrated  by  the  zinc  process. 

The.  Pattinson  process  is  not  used  in  this  country.  A  modifi- 
cation, known  as  the  "steam  Pattinson  process"  has  been  in- 
troduced by  Luce  and  Rozan,  and  adopted  in  many  European 
works.  This  consists  in  melting  the  bullion  and  trans- 
ferring it  to  a  special  form  of  crystallizer,  from  which  both  the 
enriched  bullion  and  the  lead  are  withdrawn  in  the  molten  con- 
dition. The  crystallizer  is  a  cylindrical,  flat-bottomed  vessel, 
heated  independently  and  is  provided  with  steam  connection, 
doors  at  the  top  for  introducing  the  charges  and  slide-valves 
at  the  bottom  for  emptying.  It  is  covered  with  a  hood  which 
terminates  in  a  flue  for  carrying  off  the  fume.  Two  pans  are 
used  for  melting  the  lead,  and  these  are  so  placed  that  they  can 
be  tipped  to  transfer  the  contents  to  the  crystallizer. 

The  charge  having  been  received,  a  jet  of  steam  under  45 
pounds  pressure  is  turned  on  the  surface  of  the  lead  in  the  crys- 
tallizer. The  steam  cools  the  lead  and  causes  a  regular  separa- 
tion of  crystals,  besides  aiding  in  the  removal  of  impurities  in 
the  dross.  When  two  thirds  of  the  charge  have  been  crystal- 
lized the  steam  is  shut  off  and  the  liquid  portion  is  drawn  out. 
The  crystals  are  then  remelted  and  the  deficiency  in  the  charge 
is  made  up  with  lead  of  the  same  tenor  in  silver.  The  opera- 
tion is  repeated  until  the  alloy  is  rich  enough  to  cupel.  Eleven 
crystallizations  are  required  to  render  the  lead  sufficiently  pure, 


LEAD  REFINING  2.2.J 

if  to  begin  with,  it  contains    146.12    ounces    of   silver   per    ton, 
(Hofman). 

2.     By  the  Parkes  Process 

In  1850  Alexander  Parkes,  of  Birmingham,  England,  obtain- 
ed a  patent  for  separating  silver  from  lead,  which  patent  recog- 
nized the  principles  upon  which  this  process  is  based.  As  has 
elsewhere  been  stated  lead  and  zinc  do  not  alloy  in  the  true 
sense — from  a  molten  mixture  they  separate  almost  completely. 
Silver  alloys  with  zinc  more  readily  than  it  does  with  lead ;  there- 
fore, if  zinc  is  melted  with  lead  and  silver,  the  zinc  upon  separat- 
ing, carries  most  of  the  silver  with  it.  These  facts  are  made  use  of 
in  the  Parkes  process,  or  it  is  often  called,  the  zinc  process. 

The  arrangement  of  the  refining  and  desilverizing  plant  is 
shown  in  Figs.  76  and  77.  It  consists  essentially  of  softening 


Fig.  76— Plan  of  Parkes  Desilverizing  Plant. 

a,  softening  furnace  ;  b,  zincing  and  liquating  kettles ;  c,  refining  furnaces ; 
d,  merchant  kettles. 


— Section  on  CD. 

furnaces,  desilverizing  and  liquating  kettles,  refining  furnaces, 
merchant  kettles  and  accessory  apparatus  for  handling  the  lead. 
With  this  terraced  arrangement  of  the  furnaces  and  kettles  the 
lead  is  transferred  after  each  operation  by  gravity. 

Desilverization. — The  lead  is  first  softened  in  the  usual  way. 
From  the  softening  furnace  it  is  tapped  into  the  large  30  to  50 
ton  kettles.  It  is  heated  above  the  melting  point  of  zinc,  and 
any  dross  that  has  formed  is  skimmed  off.  A  definite  quantity 
of  zinc  is  now  added,  and  when  melted,  thoroughly  mixed  with 


228  METALLURGY 

the  lead  by  stirring.  This  requires  about  three-quarters  of  an  hour 
and  is  very  trying  labor.  Mechanical  stirrers  and  steam  are  now 
used  by  many  operators.  The  quantity  of  zinc  added  is  gaged 
according  to  the  content  of  silver.  Roswag's  formula  calls  for 
zinc  as  follows : 

Z  =  23.32  +  0.223  T. 

Z  stands  for  pounds  of  zinc  and  T  for  ounces  of  silver  per  ton 
of  lead.  After  stirring  in  the  zinc  the  bath  is  allowed  to  cool 
quietly  for  from  two  to  three  hours.  The  zinc  gradually  rises 
arid  forms  a  crust  upon  the  surface  of  the  lead.  The  crust  is 
broken  up  and  removed  by  means  of  a  perforated  skimmer,  the 
lead  being  allowed  to  drain  back  into  the  kettle.  An  improved 
skimmer  is  now  used  at  many  works.  It  is  cylindrical  in  shape 
and  is  fitted  with  a  screw  press  for  squeezing  the  lead  out  of 
the  crusts.  The  perforated  bottom  is  hinged  so  that  it  can 
be  opened  to  discharge  the  crusts.  The  rich  zinc  crusts  handled 
in  this  way  may  be  distilled  without  any  further  liquation  of 
the  lead. 

Unless  the  lead  is  very  poor  in  silver  one  zincing  will  not  be 
sufficient.  To  continue  the  desilverization  the  kettle  is  again 
heated  and  the  operation  is  continued  as  before.  Three  or  four 
additions  of  zinc  may  be  necessary.  The  crusts  from  each  zinc- 
ing must  obviously  be  poorer  in  silver  than  those  previously 
obtained.  Those  of  the  last  zincing  may  be  used  in  the  zincing 
of  a  fresh  charge  of  lead.  Samples  of  the  lead  are  assayed 
before  each  addition  to  determine  how  much  zinc  is  needed. 

Distillation. — The  zinc  crusts,  if  handled  with  the  alloy  press, 
are  charged  directly  into  the  distillation  furnace.  A  further 
separation  of  lead  is  necessary  if  they  are  taken  from  the  ket- 
tle in  the  old  way.  They  are  heated  in  the  smaller  kettle  above 
the  melting  point  of  lead,  and  the  lead  runs  away  through  an 
opening  into  the  smallest  kettle.  The  separation  of  the  lead 
from  the  alloy  is;  of  course,  not  complete.  The  liquated  lead  is 
returned  to  the  desilverizing  kettle  and  the  alloy  is  distilled. 

For  the  distillation  of  the  zinc  from  the  crusts  a  small  re- 
tort furnace  is  used.  The  furnace  consists  of  a  cubic  combus- 
tion chamber,  in  which  a  graphite  retort  is  supported  in  the  in- 


LEAD  REFINING 


229 


clined  position — mouth  upward.  The  retort  is  pear-shaped,  and 
it  may  be  provided  with  a  tap-hole  in  the  bottom.  The  neck 
of  the  retort  passes  through  the  wall  of  the  heating  chamber 
and  into  the  condenser,  the  joint  between  the  two  being  care- 
fully luted  with  clay.  Old  retorts  and  crucibles  are  commonly 
used  as  condensers.  The  furnace  is  held  together  by  an  iron 
frame  and  is  swung  on  trunnions  so  that  the  contents  of  the  re- 
tort may  be  poured  out.  Stationary  furnaces  are  also  in  use. 
The  furnace  is  commonly  heated  with  gas  or  oil. 

The  zinc  that  is  distilled  from  the  crusts  and  condensed  car- 
ries some  lead  and  a  small  amount  of  silver  with  it.  It  is  used 
again  in  the  desilverizing  kettle.  The  residue  'containing  the 
lead  and  silver  is  tapped  or  poured  from  the  retort,  and  the 
lead  is  separated  by  cupellation. 


Fig.  78. 

Cupellation. — The  final  separation  of  silver  and  lead  is  one 
in  which  the  enriched  alloy  is  melted  in  an  oxidizing  atmosphere, 
the  lead  being  oxidized  and  the  oxide  removed  by  volatilization, 
absorption  and  skimming.  Fig.  78  represents  a  cupellation 
furnace.  It  is  a  small,  reverberatory  furnace  into  which 
air  is  admitted  freely  with  the  flame.  The  hearth  con- 
sists of  a  cast  iron  test-plate,  having  a  concave  bottom, 
and  a  lining  of  such  material  as  fire-clay,  limestone  and 
Portland  cement.  The  older  and  more  expensive  hearths  con- 
sisted of  wrought  iron  plates  and  bone  ash  linings.  The  shape 
of  the  hearth  varies  from  oval  to  rectangular  and  square.  The 
roof  of  the  furnace  dips  close  to  the  hearth,  and  the  flue  leads 
directly  downward.  Air  is  blown  in  upon  the  charge  to  hasten 
oxidation. 

The  furnace  being  at  a  dull-red  heat,  the  silver-lead  alloy 
is  charged  and  melted  down.  The  blast  is  then  turned  on,  and 


230  METALLURGY 

the  lead  oxide  which  rapidly  coats  the  surface  of  the  bath  is 
driven  forward.  The  fused  oxide  is  drawn  off  into  an  iron 
kettle,  and  a  portion  of  it  is  volatilized  and  carried  down  the 
flue  which  leads  to  fume  chambers.  The  cupellation  is  usually 
finished  and  the  silver  refined  in  a  separate  furnace,  the  first 
operation  being  the  concentration  of  the  bullion  to  upwards  of 
70  per  cent,  silver.  The  concentrating  process  is  continuous, 
lead  being  supplied  as  fast  as  it  is  oxidized. 

The  lead,  after  it  has  been  desilverized  by  the  Parkes  pro- 
cess, retains  from  0.6  to  0.7  per  cent,  of  zinc.  With  the  plant  ar- 
rangement above  described  it  is  siphoned  from  the  kettles  into  the 
refining  furnaces  and  refined  in  the  usual  way.  Any  copper  and 
gold  present  will  have  been  removed  with  the  first  zinc  crusts. 
The  zinc,  arsenic  and  other  impurities  are  separated  with  the 
dross  of  the  refining  furnace.  The  lead  is  finally  tapped  into 
the  merchant  kettles  where,  after  cooling  to  the  proper  tempera- 
ture for  casting,  it  is  cast  into  pig  molds  for  the  market. 

ELECTROLYTIC  REFINING 

Lead  may  be  purified  tc  a  very  high  degree  by  electrolysis. 
A  number  of  processes,  making  use  of  this  principle,  have  been 
proposed,  but  the  cost  has  not  yet  been  sufficiently  reduced  to 
warrant  the  substitution  of  electrolytic  methods  for  those  in 
general  use.  One  process,  which  has  been  used  at  Rome,  New 
York,  was  designed  for  the  treatment  of  work  lead.  The  lead 
is  cast  into  anodes,  and  these  are  suspended  in  a  solution  of 
lead  sulphate  in  sodium  acetate.  The  cathodes  are  of  sheet 
brass.  By  the  action  of  the  current  the  lead  is  dissolved  and 
deposited  from  the  solution  in  almost  a  pure  state.  The  silver 
and  gold  are  left  unattacked,  and  the  other  metals  are  either 
dissolved  or  deposited  in  the  anode  mud.  The  anodes  are  usual- 
ly enclosed  in  muslin  bags  to  keep  the  precious  metals  from 
being  carried  away  with  the  solution. 

In  another  process  for  refining  lead  an  electrolyte  of  lead 
fluo-silicate  containing  an  excess  of  fluo-silicic  acid  is  used.1 


1  Trans.  Amer.  Inst.  Min.  Eng.,  34,  175. 


CHAPTER  XXIII 


ZINC 

History. — Zinc  is  generally  considered  as  being  among  the 
modern  metals,  since  but  little  was  known  of  it  as  a  distinct 
metal  until  the  i6th  century.  It  was  used  for  making  brass  for 
many  years  before  it  was  recognized  as  a  separate  metal.  The 
Chinese  were  perhaps  the  first  to  extract  zinc  from  its  ores.  In 
fact,  it  is  believed  that  the  first  process  employed  in  Europe  for 
smelting  zinc  was  borrowed  from  China.  The  first  important 
zinc  works  were  erected  by  John  Champion,  an  Englishman, 
his  process  continuing  in  use,  with  some  modifications,  until 
1860.  The  Belgian  process  was  originated  by  Dony,  a  Belgian 
chemist,  in  1805.  This  process  is  now  in  general  use.  Zinc 
smelting  was  begun  in  the  United  States  in  1850. 

ORES 

Sphalerite  (ZnS),  commonly  knowtn  as  Blende,  is  the  most 
important  ore  of  zinc.  It  occurs  in  rocks  of  all  ages  and  is 
rarely  ever  pure.  It  is  often  associated  with  ores  of  lead  and 
iron,  more  rarely  with  copper  and  silver. 

Smithsonite  (ZnCO3)  occurs  usually  in  calcareous  rocks,  and 
is  often  associated  with  other  zinc  ores.  It  is  widely  distributed 
but  is  not  often  an  abundant  ore. 

Willemite  (2ZnO.SiO2)  is  an  important  ore  in  some  localities. 
Like  smithsonite  it  is  often  associated  with  other  ores. 

Calamine  is,  strictly  speaking,  the  hydrated  silicate  of  zinc. 
It  is  commonly  understood  to  include  the  carbonates  and  sili- 
cates of  zinc,  which  are  generally  associated  and  of  quite 
variable  composition. 

Franklinite  is  an  ore  occurring  in  New  Jersey.  It  is  a  mix- 
ture of  zincite  (ZnO)  with  the  magnetic  oxide  of  iron  and  the 
corresponding  oxide  of  manganese. 

The  principal  known  deposits  of  zinc  in  America  are  in  the 
Middle  states  and  New  Jersey.  The  only  other  Eastern  de- 


232  METALLURGY 

posits  that  are  mined  are  in  Virginia  and  Tennessee.  Kansas 
now  leads  all  other  states  in  the  production  of  zinc,  Illinois, 
holding  second  place. 

PROPERTIES 

Zinc  is  of  a  bluish-white  color  and  takes  a  high  polish.  The 
fracture  is  granular  or  highly  crystalline,  depending  upon  the 
manner  of  cooling.  The  tenacity,  as  given  by  Robert's-Austen, 
is  from  7,000  to  8,000  pounds  per  square  inch.  Zinc  is  ductile 
and  malleable  at  ioo-i5O°C.,  though  brittle  at  ordinary  tempera- 
tures. It  is  even  more  brittle  at  a  temperature  just  below  the 
melting  point.  The  melting  point  is  415°  and  the  boiling  point 
920°.  Zinc  makes  good  castings,  as  it  contracts  but  slightly  on 
cooling  and  does  not  occlude  gases  to  any  great  extent.  It  al- 
loys readily  with  most  metals  except  lead. 

Chemical. — Zinc  is  unaltered  in  pure,  dry  air.  In  moist  air, 
containing  carbon  dioxide  it  becomes  coated  with  basic  zinc 
carbonate,  which  coating  protects  the  metal  from  further  action. 
The  mineral  acids  dissolve  zinc,  and  from  some  solutions  it  is  pre- 
cipitated by  the  electric  current.  All  the  common  metals  except 
iron  and  nickel  are  precipitated  from  their  solutions  by  zinc. 
At  a  temperature  slightly  above  its  melting  point  zinc  burns  in 
the  air,  forming  the  well  known  oxide  (ZnO).  The  oxide  is  in- 
fusible at  furnace  temperatures  though  it  forms  a  slag  with 
silica  which  fuses  at  a  much  lower  temperature.  Zinc  oxide  may 
be  reduced  with  carbon,  hydrogen  and  iron.  The  affinity  of  zinc 
for  sulphur  is  not  so  strong  as  that  of  copper  and  iron.  When 
zinc  sulphide  is  roasted  in  air  it  is  converted  into  the  oxide  and 
sulphate. 

Impurities  in  Zinc. — Commercial  zinc  is  known  as  "spelter." 
It  is  apt  to  contain  lead,  iron  and  cadmium,  and  often  smaller 
quantities  of  arsenic,  antimony  and  other  elements.  Lead  is 
the  most  common  impurity,  a  small  amount  in  many  cases  not 
being  objectionable,  since  it  actually  increases  malleability  and 
ductility.  The  presence  of  foreign  elements  in  general  renders 
zinc  brittle,  weak  and  unfit  for  the  manufacture  of  alloys  and 
for  plating — its  principal  uses. 


ZINC  233 

PREPARATION  OF  ZINC  ORES  FOR  SMELTING 

Mechanical  Concentration. — Under  this  head  may  be  men- 
tioned washing  and  magnetic  concentration,  also  crushing 
which,  if  not  essential  to  the  process  of  dressing  the  ore,  is 
always  essential  to  smelting.  Ores  which  contain  light,  earthy 
material  may  be  washed,  and  those  containing  much  iron  oxide 
may  be  concentrated  with  magnetic  machines. 

Calcining  and  Roasting. — Oxidized  ores  are  calcined  to  drive 
oft  water  (water  of  hydration)  and  carbon  dioxide.  This 
practice  is  not  followed,  however,  unless  there  is  an  abundance 
of  the  ore  and  it  is  to  be  smelted  without  the  admixture  of 
roasted  ore.  Water  vapor  .and  carbon  dioxide  are  objectionable 
in  zinc  smelting  as  will  be  explained  later. 

Blende  is  always  roasted  before  smelting.  It  is  essential  that 
the  roasting  be  thorough,  since  the  amount  of  zinc  that  is  left 
in  the  residues  after  smelting  is  largely  proportional  to  the 
amount  of  sulphur  that  is  charged  with  the  ore.  Zinc  ores  are 
always  roasted  in  the  pulverized  condition.  Hand-raked  and 
mechanically-raked  reverberatory  furnaces  are  generally  em- 
ployed. The  Brown  roaster,  of  the  type  described  in  Chapter 
XVII,  is  used  in  the  West,  where  large  quantities  of  ore  are 
treated.  Revolving,  muffle  and  shaft  furnaces  are  also  in  use. 

W.  P.  Blake1  has  described  a  process  by  which  he  treats 
blende  that  is  associated  with  iron  pyrites  and  galena.  After 
a  preliminary  crushing  and  concentrating  with  jigs  the  ore  is 
carefully  roasted  to  decompose  the  pyrite.  The  iron  should  be 
completely  desulphurized,  though  the  blende  remains  practically 
unaltered.  The  roasted  ore  is  jigged  again  to  separate  the 
light  oxide  of  iron  from  the  blende  and  any  galena. 

Pyritous  ores  of  zinc  and  lead  may  be  concentrated  by  roast- 
ing at  a  low  temperature  to  convert  the  iron  into  the  magnetic 
form,  and  then  passing  the  fine  ore  through  magnetic  machines. 

Some  zinc  compounds  are  lost  during  the  roasting,  being  car- 
ried away  as  dust  with  the  smoke.  For  this  reason  the  tem- 
perature is  kept  as  low  as  possible,  and  the  ore  is  not  allowed 
to  remain  in  the  roaster  any  longer  than  is  necessary.  The  dust 
is  collected  in  chambers  built  between  the  furnace  and  the  stack. 
1  Trans.  Amer.  Inst.  Min.  Eng.,  22,  569. 


234  METALLURGY 

ZINC  SMELTING 

The  Manufacture  of  Retorts  and  Condensers. — A  pottery  is 
built  in  connection  with  the  zinc  smelting  works.  It  is  of  prime 
importance  that  the  clay  for  making  the  retorts  be  of  the  proper 
composition  and  texture.  Besides  its  refractory  qualities  the 
retort  must  retain  considerable  tensile  strength  in  the  furnace, 
at  the  same  time  permitting  the  walls  to  be  made  thin  enough 
to  be  easily  permeable  to  heat,  and  they  must  be  as  non-porous 
as  possible  to  prevent  the  escape  of  zinc  vapors.  The  clays 
used  in  this  country  come  mostly  from  New  Jersey  and  Mis- 
souri, some  analyses  of  which  average  as  follows:1 

SiO2  A12O3         Fe2O3        CaO          MgO    K2O.Na2O  TiO2         H2O 

N.  J...     45-          37-5          0.7          i  0.3          0.5        1.5        13.5 

(I^ossby  ignition) 

Mo.  ..     49.5        34.46        2.39        0.8        0.62  12.86 

On  account  of  the  high  shrinkage  of  clay,  retorts  are  not  made 
of  the  raw  material  alone,  but  this  is  mixed  with  from  50  to  60 
per  cent,  of  old  retorts  or  burnt  clay  (chamott).  In  preparing 
the  material  for  the  retorts  the  chamott  and  clay  are  separately 
crushed  to  the  proper  size  and  then  mixed  by  shovelling  on 
the  floor.  The  mixture  with  just  enough  water  to  develop 
plasticity  is  fed  into  a  mechanical  mixer  and  pug  mill.  The 
pug  mill  is  essentially  a  steel  or  cast  iron  cylinder  in  which  a 
longitudinal  shaft  carrying  knives  revolves.  The  knives  may 
be  set  at  different  angles  to  regulate  the  rate  of  pugging.  The 
cylinder  is  stationary  and  is  either  in  the  horizontal  or  the  ver- 
tical position.  It  is  made  in  removable  sections  and  is  slightly 
contracted  toward  the  discharge  end.  This  feature  effects 
some  compression  of  the  clay.  The  machine  is  provided  with  a 
hopper  from  which  the  clay  is  taken  in  by  means  of  a  screw, 
terminating  with  the  first  knife.  The  end  of  the  cylinder  at 
which  the  clay  is  discharged  is  bent  at  right  angle,  and  the 
mouth  is  contracted  to  regulate  the  discharge.  As  the  pugged 
clay  flows  from  the  mill  an  attendant  breaks  it  in  pieces  which 
have  approximately  the,  weight  of  a  retort. 

Retorts  are  made  almost  entirely  by  machinery.     The  auger 
machine,  or  one  of  this  type,  is  commonly  used  in  this  country 
1  Ingalls,  "  Metallurgy  of  Zinc  and  Cadmium." 


ZINC  235 

The  clay  is  charged  into  an  upright  cylinder  by  means  of  a 
belt  elevator.  A  revolving  shaft  passing  through  the  cylinder 
carries  knives  which  are  so  set  that  they  force  the  clay  down- 
ward as  they  revolve.  The  clay  flows  around  a  core,  which  is 
centered  to  form  the  interior  of  the  retort  tube.  As  the  tube 
of  clay  is  pushed  downward  out  of  the  machine  it  is  supported  on 
a  counterpoise"  pallet,  which  permits  it  to  descend  only 
so  fast  as  it  is  finished.  When  enough  of  the  tube  has  been 
made  for  a  retort  the  machine  is  stopped  and  the  tube  is  cut  with 
a  small  wire.  A  wooden  form  is  placed  ready  to  receive  the 
retort.  The  object  in  using  the  form  is  to  support  the  walls  of 
the  retort  and  to  prevent  injury  while  it  is  being  handled.  The 
end  of  the  retort  is  closed  after  it  has  been  placed  in  the  form 
by  tamping  in  a  disc  of  clay. 

Retorts  are  now  made  in  hydraulic  machines  at  some  works. 
These  machines  are  more  expensive  but  they  make  better  re- 
torts. The  clay,  being  more  compressed,  is  less  porous  and 
therefore  less  permeable  to  gases,  which  means  greater  economy 
in  distilling.  No  form  is  needed  for  retorts  made  in  high  pres- 
sure machines. 

Form  mid  Size  of  Retorts. — The  circular  and  elliptical  re- 
torts are  the  only  styles  used  in  this  country.  The  circular 
ones  are  about  50  inches  in  length  and  8  inches  in  diameter,  and 
the  elliptical  ones  about  54  inches  in  length  and  10  x  8  inches  in 
•diameter.  There  is  but  little  advantage  of  one  form  over  the 
other.  The  elliptical  shape  obviously  lends  more  transverse 
strength  to  the  retort  as  it  is  supported  in  the  furnace.  Some 
smelters  use  both  kinds,  placing  the  round  ones  in  the  upper 
rows  and  the  elliptical  ones  below,  the  idea  being  that  in  direct- 
fired  furnaces  the  lower  retorts  are  exposed  to  the  highest  tem- 
perature, and  are  therefore  the  more  weakened,  and  that  the 
round  ones  are  easier  to  heat. 

The  clay  for  the  condensers  is  prepared  as  above  described, 
but  the  condensers  are  usually  made  by  hand,  with  the  aid  of 
a  simple  mold.  The  condensers  are  sometimes  fitted  with  a 
cone  of  sheet  iron,  known  as  a  prolong.  The  prolong  is  placed 
over  the  mouth  of  the  condenser  to  collect  escaping  vapor  of 
2.  inc. 


236  METALLURGY 

Drying  and  Annealing. — After  being  removed  from  the 
forms,  the  retorts  are  left  in  the  drying  room  for  several  weeks. 
It  is  essential  that  they  should  dry  slowly  and  evenly,  since 
they  are  apt  to  crack  at  this  tender  stage  if  one  part  dries  more 
rapidly,  and  consequently  contracts  more  rapidly  than  another. 
The  retorts  are  carefully  annealed  by  heating  them  slowly  to 
full  redness  and  keeping  them  at  this  temperature  for  some  time. 
The  annealing  furnace  is  similar  to  any  drdinary  pottery  kiln, 
and  it  is  built  near  the  distillation  furnace  for  convenience.  At 
some  plants  the  waste  heat  from  the  distillation  furnaces  is  used 
for  annealing. 

The  annealed  retorts  are  put  immediately  into  use.  The  con- 
densers are  similarly  treated,  though  less  care  is  necessary,  as 
they  are  not  exposed  to  such  high  temperatures  in  actual  use. 

The  Distillation  Furnace. — The  fact  that  zinc  is  volatile  at  a 
comparatively  low  temperature  suggests  the  best  means  of 
separating  it  from  the  ore  gangue,  viz.,  by  distillation.  Accord- 
ingly, all  zinc  smelting  furnaces  comprise  some  form  of  dis- 
tilling apparatus.  Of  these  many  forms  have  been  devised,  but 
only  one  is  in  general  use. 

The  Belgian  furnace  has  been  in  use  for  more  than  a  hun- 
dred years,  and  with  whatever  improvements  that  have  been  in- 
troduced, affecting  economy  and  output,  the  principles  are  un- 
changed. Fig.  79  gives  a  vertical  section  through  a  Belgian 
retort  furnace.  This  is  the  double  furnace,  a  type  that  is  much 
used  in  this  country.  The  walls  of  the  furnace  are  built  of 
brick,  fire-brick  being  used  above  the  fire-places .  The  retorts 
are  supported  in  the  inclined  position  by  shelves  projected  from 
the  back  walls  and  fire-clay  tiles  in  the  front  walls.  Each 
furnace  carries  seven  horizontal  rows,  arranged  in  tiers,  with 
1 6  retorts  in  each  row.  The  tiles  in  the  front  wall  are  held  in 
position  by  a  checkered,  iron  frame.  The  plates  of  which  the 
frame  is  made  are  set  edgewise  so  as  to  form  continuations  of 
the  fire-clay  shelves  holding  the  front  ends  of  the  retorts.  The 
furnace  is  supported  at  the  four  corners  by  means  of  buck- 
staves  and  tie-rods.  The  flues,  shown  at  the  top,  lead  the  prod- 


ZINC 


237 


ucts  of  combustion  into  the  central  chimney,  which  is  partly 
shown  in  elevation. 

Gas-fired  furnaces,  in  connection  with  Siemens  regenerators, 
are  in  very  general  use.  In  Kansas  furnaces  are  built  to  burn 
natural  gas. 

The  Distillation  Process. — The  retorts,  being  in  position  in 
the  furnace  and  heated  to  redness,  are  charged  with  the  ore 
mixture.  This  consists  of  the  fine  ore  mixed  with  crushed 


Fig-  79- 

anthracite.1  The  mixture  is  moistened  just  sufficiently  to  make 
it  cohere  while  charging,  and  the  retort  is  filled  rather  com- 
pactly. A  small  channel  is  made  over  the  charge  by  thrusting 
an  iron  rod  to  the  back  of  the  retort.  This  is  for  the  escape  of 
the  first  gases  of  distillation.  The  condensers  are  then  placed  in 
position  and  luted  to  the  retorts.  The  mouth  of  each  conden- 
ser is  luted  with  a  handful  of  brasque  (moist  slack).  The  re- 

1  Anthracite  containing  a  high  percentage  of  volatile  matter  is  preferred. 
In  localities  remote  from  hard  coal  deposits,  coke  mixed  with  a  small  pro- 
portion of  soft  coal  is  used. 


238  METALLURGY 

torts  in  the  upper  rows,  or  those  in  the  cooler  part  of  the  fur- 
nace are  charged  with  the  less  refractory  ore. 

The  retorts  need  but  little  attention  until  the  zinc  appears. 
When  sufficient  time  has  elapsed  for  the  gases  inside  to  have 
accumulated  with  some  pressure,  a  small  opening  is  made 
through  the  mouths  of  the  condensers,  from  which  they  escape 
and  burn  in  the  outer  air.  The  flames  which  appear  are  at 
first  yellowish,  then  bluish  and  finally  whitish.  Tinges  of  red, 
purple  and  green  also  appear.  The  luminous,  yellow  flame  is 
dt  5  to  the  hydrocarbons  evolved  at  the  beginning.  Carbon 
monoxide  gives  the  pale-blue,  and  zinc  the  greenish-white  flame 
appearing  towards  the  end  of  the  distillation.  The  smoke  is 
generally  of  a  light  color.  A  brownish  tinge  indicates  cadmium. 
Thf  effort  is  made  to  keep  the  condensers  cool  enough  to  con- 
•cler  *  all  the  zinc  vapor,  but  some  invariably  escapes.  The 
prolong  is  sometimes  put  on  to  condense  escaping  vapor  as 
before  mentioned. 

The  zinc  is  tapped  from  the  condensers  three  times  in  24 
<hours.  After  this  the  retorts  receive  a  fresh  charge.  To  tap 
the  zinc  an  iron  kettle  is  supported  under  the  mouth  of  the  con- 
denser and  the  metal  is  raked  out.  The  zinc  in  the  ladle  is 
cove  -ed  with  coal  dust  to  prevent  oxidation.  Any  cinder  or 
dross  is  skimmed  off  before  pouring.  The  zinc  is  cast  into  flat 
molds.  The  spelter  is  generally  pure  enough  for  the  market, 
though  refining  is  necessary  in  some  instances. 

There  are  some  features  of  the  Belgian  process  which  show 
poor  economy  if  not  absolute  waste.  At  the  beginning  of  the 
distillation,  when  the  reducing  gases  are  more  or  less  diluted 
with  carbon  dioxide  and  oxygen  some  of  the  zinc  becomes 
oxidized.  Being  in  the  form  of  vapor  the  zinc  is  deposited  in 
the  condenser  as  a  powder  (commonly  known  as  "blue  pow- 
der"). This  powder  assays  about  90  per  cent,  metallic  zinc, 
and  while  it  is  recovered,  it  is  necessary  to  charge  it  again  into 
the  retorts.  Some  of  the  zinc  vapor  escapes  and  burns  at  the 
mouths  of  the  condensers,  and  a  smaller  amount  diffuses 
through  the  walls  of  the  retorts.1  The  residues  left  in  the  re- 

1  An  old  retort  contains  from  six  to  ten  per  cent,   of  zinc  in  its  walls. 
At  some  works  the  retorts  are  glazed  to  prevent  the  absorption  of  zinc. 


ZINC  239 

torts  contain  variable  amounts  of  zinc,  which  is  expensive  to  re- 
cover. The  tapping  of  zinc,  cleaning  the  retorts  and  charging 
is  exceedingly  hard  labor,  and  unhealthful  as  well. 

Refining  Spelter.— There  is  but  one  process  in  general  use 
for  refining  spelter — that  of  liquation.  Redistillation  is  general- 
ly unprofitable,  resulting  in  a  high  loss  of -zinc.  In  Europe, 
where  less  pure  spelter  is  made,  and  consequently  more  refin- 
ing is  practiced,  the  spelter  is  treated  in  a  small  reverberatory 
furnace,  in  the  hearth  of  which  is  a  sump  or  well. 

The  spelter  is  melted  down  slowly,  and  oxidation  is  prevented 
as  far  as  possible  by  using  just  enough  heat  to  effect  the  fusion, 
and  by  excluding  air.  The  lead  and  some  iron  are  liquated, 
and  more  impurity  separates  with  the  dross  that  forms.  The 
zinc,  which  forms  the  upper  metal  layer,  is  ladled  or  drawn ^off, 
and  the  lead  is  taken  out  when  it  has  accumulated  in  sufifi  ient 
quantity.  It  may  be  necessary  to  further  purify  both  the  lead 
and  the  zinc  by  remelting  and  liquating.  The  lead  should  be. 
brought  down  in  the  spelter  to  at  least  1.50  per  cent.1 


1  The  tenor  of  lead  in  Bertha  spelter,  manufactured  at   Pulaski,  Va., 
that  is  run  from  lead-bearing  ores  is  uniformly  one  per  cent,  or  below. 


CHAPTER  XXIV 


TIN  AND  MERCURY 


TIN 

Cassiterite  (SnO2)  is  the  only  tin  ore  of  metallurgical  note, 
it  is  a  hard,  crystalline  mineral,  occurring  in  veins,  usually  in 
granite  or  other  rocks.  Iron,  copper  and  arsenical  pyrites, 
galena  and  wolfram  are  sometimes  associated  with  tin  ores. 
"Stream  ore"  is  that  which  has  been  carried  down  from  the 
eroded  rocks  by  water.  Tin  ore  is  found  in  Malacca,  the  East 
Indies  and  England,  and  more  sparingly  in  Germany,  Russia, 
Spain  and  Mexico.  The  famous  Cornwall  deposits  were  per- 
haps the  first  to  be  worked,  these  having  been  visited  by  the 
Phoenicians  before  the  time  of  Julius  Caesar.  No  important 
deposits  in  the  United  States  have  yet  been  found. 

Properties. — Tin  has  almost  the  whiteness  of  silver,  with  a 
faint  tint  of  yellow.  The  tenacity  is  very  low,  the  metal  break- 
ing under  a  load  of  a  little  more  than  2,000  pounds  per  square 
inch.  It  is  quite  malleable,  however,  as  may  be'  seen  from  the 
thinness  of  tin  foil.  Tin  produces  a  characteristic  crackling 
sound  when  bent.  This  is  known  as  the  "cry,"  and  is  supposed 
to  be  due  to  internal  friction.  Tin  melts  at  230° C.  It  alloys 
with  most  of  the  common  metals  and  most  readily  with  lead. 
At  high  temperatures  it  is  sensibly  volatile. 

As  to  its  chemical  behavior  tin  may  be  said  to  be  intermediate 
between  the  metals  and  the  non-metals.  It  is  basic,  like  most 
metals  toward  strong  acids,  replacing  hydrogen,  but  it  also 
combines  with  caustic  alkalies,  forming  stannates.  It  is  not 
appreciably  dissolved  by  organic  acids  nor  is  it  affected  in  dry 
or  moist  air  at  ordinary  temperatures.  It  is  oxidized  by  nitric 
acid,  and  by  air  at  temperatures  above  its  melting  point.  The 
oxide  is  reduced  by  carbon  at  a  moderately  high  temperature. 
Tin  combines  readily  with  sulphur,  but  the  sulphide  is  decom- 
posed by  roasting,  yielding  stannic  oxide  and  sulphur  dioxide. 


TIN    AND    MERCURY  24! 

Smelting. — Tin  ores  usually  require  a  good  deal  of  concen- 
tration before  they  can  be  properly  smelted.  The  ore  is  first 
crushed  and  washed,  and  then  roasted  to  convert  the  heavy 
arsenides  and  sulphides  into  oxides  and  sulphates.  The  soluble 
sulphates  are  removed  by  leaching  and  the  lighter  oxides  are 
separated  from  the  heavy  tin  oxide  by  gravity  washing.  The 
concentrate  thus  obtained  is  known  as  "black  tin." 

If  the  ore  contains  tungsten  in  considerable  proportion  some 
special  treatment  is  needed.  The  concentrate  is  heated  with 
salt  cake  or  soda  ash  in  sufficient  quantity  to  combine  with  all 
the  tungsten.  When  the  mass  softens  it  is  transferred  without 
cooling  to  a  lixiviating  tank  and  thoroughly  washed.  The 
tungstate  of  soda,  which  was  formed  during  the  fusion,  is  dis- 
solved, and  the  iron  and  manganese  are  thrown  down  as  oxides 
with  the  tin.  The  oxides  are  separated  as  described  above. 

in  England  the  reduction  of  tin  is  conducted  in  reverberatory 
furnaces.  A  mixture  of  about  one  ton  of  black  tin  with  400 
pounds  of  anthracite  is  treated  at  one  time.  The  proper  fluxing 
agents  are  added  and  the  furnace  is  made  as  nearly  air-tight  as 
possible  during  the  heating  to  prevent  oxidation  of  the  tin. 
The  charge  melts  down  and  the  tin  that  is  reduced 
collects  under  the  slag.  After  several  hours  of  heating  the 
bath  is  well  stirred,  and  the  tap-hole  is  opened  at  the  end  of  the 
operation,  the  tin  being  received  in  an  outside  kettle.  If  fairly 
pure  the  tin  is  refined  in  the  kettle  immediately,  otherwise  it  is 
cast  into  molds  and  subjected  to  further  treatment.  The  residue 
in  the  furnace  generally  contains  too  much  tin  to  be  thrown  away 
and  is  resmelted. 

Refining. — Two  operations  are  in  use  for  refining  very 
impure  tin.  It  is  first  "sweated"  by  a  method  similar  in  principle 
to  that  for  separating  lead  and  copper.  The  pigs  are  carefully 
heated  in  a  reverberatory  furnace  with  a  sloping  hearth.  The 
tin,  being  of  the  lowest  fusion  point,  melts  and  runs  away,  leav- 
ing a  more  or  less  porous  mass  of  unfused  metals.  This,  of 
course,  retains  some  of  the  tin,  and  is  treated  for  the  recovery  of 
all  valuable  metals. 

The  second  operation  called  "boiling"  is  conducted  in  an  iron 


242  METALLURGY 

kettle.  The  tin  is  melted  and  agitated  for  several  hours  by 
"tossing"  or  by  "polling".  In  the  former  method  a  portion  of 
the  tin  is  ladled  out  and  poured  back  into  the  kettle;  in  the 
latter  green  timber  is  held  under  the  surface  of  the  metal,  and 
the  liberated  gases  effect  the  agitation.  The  scum  which  forms 
is  skimmed  off,  and  the  process  is  continued  until  the  tin  is  suf- 
ficiently pure.  The  principle  of  this  treatment  lies  not  so  much, 
in  the  oxidation  of  the  other  metals,  for  tin  is  more  easily 
oxidized  than  most  of  them,  as  in  the  separation  of  the  other 
metals  with  higher  melting  points  than  tin  by  surface  chilling. 
Uses. — The  principal  uses  of  tin  are  in  the  manufacture  of 
alloys  and  for  plating  other  metals,  especially  iron.  The  manu- 
facture of  tin  plate  is  described  in  Chapter  XXVIII. 

MERCURY 

This  metal  is  often  called  "quicksilver"  on  account  of  its 
silvery  whiteness  and  luster,  and  its  mobility.  It  occurs  native 
in  amalgams  or  in  globules,  usually  associated  with  other  ores, 
and  as  the  sulphide.  Cinnabar  (HgS)  is  the  only  important 
ore  of  mercury.  It  is  of  very  irregular  composition  and  is  met 
with  in  Spain,  South  America,  Mexico  and  the  United  States. 
The  largest  United  States  deposits  are  in  California,  though 
mercury  ores  are  mined  in  Texas  and  other  states. 

Properties. — Mercury  is  a  white  metal  of  very  high  luster. 
It  melts  at  — 39°  and  boils  at  about  360° C.  It  is  slightly 
volatile  at  ordinary  temperatures.  The  alloys  of  mercury  are 
called  amalgams.  These  may  be  made  directly  with  most  of 
the  common  metals,  though  some  can  only  be  prepared  by  de- 
composing their  salts.  Silver  and  gold  are  especially  active 
toward  mercury.  The  low  specific  heat,  mobility,  conductivity 
and  high  specific  gravity  render  mercury  peculiarly  fitted  for 
the  manufacture  of  scientific  apparatus. 

Mercury  is  not  oxidized  by  dry  air  at  ordinary  temperatures, 
but  when  heated  to  350°  C.  it  is  slowly  converted  into  the  red 
oxide  (HgO).  At  higher  temperatures  it  is  reduced  to  metal- 
lic mercury.  Nitric  acid  and  hot  sulphuric  acid  dissolve  mercury 
readily,  but  hydrochloric  acid  has  very  little  action  with  it. 
The  sulphide  of  mercury  is  volatile  and  is  readily  decomposed 


TIN  AND  MERCURY  243 

by  roasting,  yielding  metallic  mercury  and  sulphur  dioxide  (the 
temperature  being  too  high  for  the  existence  of  mercuric 
oxide).  Cinnabar  is  more  completely  decomposed  when  heated 
with  lime. 

Smelting. — The  extraction  of  mercury  from  its  ores  is 
theoretically  a  simple  matter.  It  involves  the  decomposition  of 
the  ore  by  heat  and  the  condensation  of  the  mercurial  vapors. 
The  latter  problem  offers  some  difficulty.  It  is  necessary  that 
the  condenser  be  spacious,  for  a  very  large  volume  of  gases 
must  be  dealt  with,  and  that  it  be  impervious  to  the  vapor  of 
mercury,  which  is  poisonous.  The  condensers  can  not  be  made 
of  iron  throughout,  on  account  of  the  acid  in  the  vapors.  Any 
masonry  employed  must  be  most  carefully  constructed.  Glazed 
earthen-ware  and  glass  are  used  at  some  plants. 

A  great  many  styles  of  furnaces  have  been  introduced,  and 
a  number  are  now  in  use  for  smelting  cinnabar.  The  ore  is 
commonly  decomposed  in  shaft  or  reverberatory  furnaces 
through  which  a  forced  draft  is  maintained  to  drive  the  prod- 
acts  of  oxidation  and  distillation  into  suitable  condensers.  Shaft 
furnaces  have  generally  met  with  favor  because  they  are  adaptable 
to  the  treatment  of  both  coarse  and  fine  ore.  Externally  heated 
retorts  are  seldom,  used.  The  Spirek  furnace  may  be  taken  as 
a  representative  of  modern  furnaces.1  It  consists  of  a  double 
shaft  for  decomposing  the  ore,  and  a  condensing  apparatus. 
The  vertical  section  (Fig.  80)  is  through  one  of  the  shafts 
and  one  set  of  the  condensers.  The  furnace  proper  is  built  of 
brick  reenforced  with  iron.  The  furnace  walls  are  supported 
on  brick  pillars  resting  on  a  concrete  foundation.  Sheets  of 
iron  turned  up  at  the  edges  are  placed  underneath  the  pillars 
to  catch  mercury,  and  a  drain  is  made  in  the  foundation  to 
prevent  loss  from  leakage.  The  ore  is  charged  into  the  fur- 
nace from  a  hopper  at  the  top,  a  special  device  being  used  to 
prevent  the  escape  of  mercurial  vapor.  The  charge  is  car- 
ried on  sloping  bars  which  can  be  removed  for  taking  out  spent 
residues. 

Enough  fuel  is  mixed  with  the  charge  to  decompose  the  ore 
1  The  Min.  Ind.,  1902,  559. 


244 


METALLURGY 


and  volatilize  the  mercury.  Air  is  drawn  through  the  fur- 
nace by  means  of  a  fan.  The  mercury  vapor  together  with  a 
large  volume  of  sulphur  dioxide  and  other  products  of  com- 
bustion is  led  through  the  downtake  into  the  condenser.  The 
condenser  is  of  sufficient  capacity  to  cool  down  the  gases  by 
contact  with  its  walls  until  their  temperature  is  below  the 
liquefying  point  of  mercury.  It  consists  of  a  number  of  inverted 
U-tubes,  arranged  as  shown,  with  the  ends  opening  into  hoppers, 
the  funnels  of  which  dip  under  water.  The  water  is  held  in  iron 
boxes.  The  condenser  tubes  are  elliptical  in  cross-section,  and 


Fig.  80. 

are  constructed  of  iron  lined  on  the  interior  with  concrete. 
When  comparatively  cool,  the  smoke  is  led  into  wooden  flues 
in  which  soot  is  deposited,  and  from  which  a  small  amount  of 
mercury  is  obtained.  Doors  are  located  at  convenient  points 
in  the  condensers  for  cleaning. 

Mercury  is  refined  by  straining  to  separate  undissolved  mat- 
ter, and  by  redistillation  from  dissolved  metals.  Small  amounts 
may  be  purified  by  shaking  with  nitric  acid. 

Uses. — Mercury  is  shipped  in  screw-stoppered,  iron  flasks, 
usually  weighing  75  pounds  each.  Its  chief  use  is  in  the  'ex- 
traction of  silver  and  gold.  It  is  also  used  for  mating  mirrors, 
in  amalgams  and  in  the  manufacture  of  scientific  apparatus. 


CHAPTER  XXV 


SILVER 

ORES 

Native. — Silver  occurs  native  in  small  quantities,  and  as  such 
is  usually  associated  with  other  ores.  It  is  found  in  Lake 
copper  and,  in  general,  it  occurs  in  silicious  rocks,  not  infre- 
quently with  a  small  amount  of  gold.  Silver  amalgam  also  oc- 
curs. 

Argentite  (Ag2S)  is  the  most  common  ore  of  silver.  When 
isolated  it  is  a  grayish-black  substance,  sectile  and  readily 
fusible.  It  occurs  in  silicious  and  other  rocks,  and  is  often  as- 
sociated with  pyrites,  galena  and  other  sulphides. 

Horn  Silver  (AgCl)  occurs  in  Mexico  and  South  America, 
and  is  often  a  very  valuable  ore.  The  bromide  and  iodide  are 
also  met  with. 

Tetrahedrite  was  mentioned  under  the  ores  of  copper.  It  is 
often  worked  for  the  silver  value  rather  than  for  the  copper. 

Mexico  is  the  leading  silver  producing  country.  Silver  is 
mined  extensively  in  the  Western  states,  Colorado  leading  in 
output. 

PROPERTIES 

Silver,  when  pure,  is  the  whitest  of  the  metals,  and  it  takes 
a  very  high  polish.  It  is  tenacious,  highly  ductile  and  mal- 
leable, being  exceeded  only  by  gold  in  the  latter  property.  Be- 
ing too  soft  when  pure  for  most  purposes,  silver  is  commonly  al- 
loyed with  copper.  The  melting  point  of  silver  is  950° C. ;  it 
alloys  with  most  metals,  and  readily  amalgamates  with  mercury. 
While  in  the  molten  state  silver  is  capable  of  dissolving  more 
than  20  times  its  own  volume  of  oxygen.  In  conductivity  it 
excels  all  other  metals. 

Chemical  Properties  Relating  to  Metallurgy. — Silver  can  not 
be  oxidized  directly.  It  is  soluble  in  nitric  acid  and  less 
readily  in  sulphuric  acid.  It  is  not  appreciably  attacked  by 
hydrochloric  acid,  but  silver  chloride  is  formed  by  the  double 


246  METALLURGY 

decomposition  of  a  silver  ^alt  with  the  chloride  of  another  metal 
or  by  the  direct  action  of  chlorine  gas  on  metallic  silver.  Sil- 
ver chloride  is  soluble  in  brine,  in  a  solution  of  sodium  or  potas- 
sium thiosulphate  and  in  rather  concentrated  hydrochloric 
acid.  Silver  is  reduced  from  the  chloride  by  nascent  hydrogen, 
by  certain  metals  and  by  fusion  with  carbonate  of  sodium.  If 
to  a  solution  of  silver  in  sodium  thiosulphate,  sodium  sulphide  is 
added,  silver  sulphide  is  thrown  down  and  the  thiosulphate  is  re- 
generated. Silver  has  a  strong  affinity  for  sulphur.  The  sulphide 
is  decomposed  by  oxidizing  roasting,  being  partially  converted 
into  the  sulphate.  This  change  takes  place  more  readily  in  the 
presence  of  other  bases. 

EXTRACTION  OF  SILVER 

The  processes  in  use  for  extracting  silver  may  be  classified 
as  follows:  I.  Smelting  Processes;  2.  Amalgamating  Pro- 
cesses; 3.  Leaching  Processes. 

i.  Smelting 

This  refers  to  the  smelting  of  copper  and  lead  ores  which 
contain  silver.  The  silver  may  be  associated  naturally  and  there- 
fore be  obtained  as  a  by-product,  or  the  other  metals  may  be 
used  as  alloying  and  dissolving  agents.  The  manufacture  of 
"work  lead"  affords  a  good  example  of  this  practice.  Silver 
ores  are  mixed  with  rich  lead  ores  and  the  mixture  is  smelted 
for  work  lead,  or  rich  silver  ore  may  be  melted  with  metallic 
lead.  The  recovery  of  silver  as  a  by-product  has  been  noted 
in  the  chapters  on  copper  and  lead  refining. 

2.  Amalgamating 

This  method  of  treatment  involves  the  amalgamation  of  the 
silver  in  the  ore;  the  separation  of  the  amalgam  from  the  ore 
gangue,  and  the  final  separation  of  the  silver  from  the  mercury. 
Silver  amalgam  is  made  directly  from  the  metal  or  from  the 
chloride.  It  is  necessary  that  the  ore  be  in  a  very  finely  divided 
state,  and  in  most  cases  the  ore  must  be  chloridized.  There 
are  two  ways  of  chloridizing  silver  ores,  viz.,  in  the  dry  way  by 
roasting  with  salt,  and  in  the  wet  way  by  mixing  with  the  ore 
a  solution  of  copper  chloride. 


SILVER  247 

Crushing. — The  ore  is  first  reduced  to  small  sizes  in  a  rock 
breaker,  and  is  then  subjected  to  finer  crushing  in  stamp  mills, 
Chilian  mills,  pans,  etc.  Descriptions  of  crushing  machinery, 
other  than  are  given  in  this  chapter  will  be  found  in  Chapter 
VI. 

Chloridizing  in  the  Dry  Way. — The  ore  for  this  method  of 
treatment  is  prepared  by  dry  stamping,  or  by  pulverizing  in 
other  ways,  and  screening  to  separate  coarse  particles.  It  is 
charged  into  reverberatory  furnaces  and  roasted  to  decompose 
the  base  sulphides,  a  low  temperature  being  employed  at  first. 
The  excessive  sulphur  being  driven  off,  salt  is  added,  and  the 
roasting  is  continued  until  the  silver  has  been  converted,  as 
far  as  possible,  into  the  chloride.  The  roasted  ore  is  again 
screened,  and  is  then  ready  for  amalgamation. 

Of  the  special  types  of  furnaces  for  chloridizing  silver  ores 
Stetefeldt's  is  the  most  important.1  It  is  a  shaft  furnace  heat- 
ed by  two  fireplaces,  the  flues  from  which  pass  into  the  shaft 
near  the  bottom.  A  mechanical  device  is  used  for  feeding  in 
the  ore  at  the  top,  and  the  bottom  of  the  furnace  terminates 
in  a  hopper  for  receiving  the  ore.  The  dust-ladened  gases 
pass  from  the  top  of  the  furnace  into  a  capacious  flue  which  is 
inclined  at  a  steep  angle.  Through  this  the  gases  are  led  into 
dust  chambers,  which  are  also  provided  with  hopper  bottoms 
for  discharging  the  accumulated  dust.  Salt  is  volatilized  in 
the  fireplaces  and  the  vapors  pass  into  the  stack  with  the  flame. 
The  fine  particles  of  ore  are  roasted  and  partially  chloridized 
during  the  few  seconds  of  the  descent,  though  about  half  of 
the  ore  is  carried  over  with  the  forced  draft.  A  separate  fire- 
place is  provided  for  roasting  the  ore  that  is  carried  into  the 
dust  chambers. 

Cylindrical  roasters  are  also  used  for  chloridizing  silver  ores, 
those  of  the  Bruckner  and  White-Howell  types  being  most 
common. 

Chloridizing  in  the  Wet  Way. — This  deals  with  the  conver- 
sion of  silver  sulphide  into  silver  chloride  by  the  reactions  with 

1  Stetefeldt's  paper,  with  illustrations — Trans.  Amer.   Inst.   Min.  Eng., 
42,3- 


248  METALLURGY 

cuprous  and  cupric  chlorides.  The  copper  chloride  is  generally 
made  by  treating  copper  sulphate  with  sodium  chloride,  the 
vitriol  being  contained  in  roasted  or  otherwise  oxidized  ores. 
The  processes  of  wet  chloridation  and  amalgamation  are  so 
closely  linked  that  they  are  most  conveniently  studied  together. 
They  will  be  described 'under  the  two  typical  processes  of  treat- 
ing silver  ores — in  the  Patio  and  in  the  Amalgamating  Pan. 

The  Patio  Process. — This  process  originated  in  Mexico  about 
the  middle  of  the  i6th  century.  It  still  survives  in  its  primi- 
tive crudeness,  owing  to  the  peculiar  conditions  there.  Some 
of  the  localities  in  which  silver  ore  abounds  are  destitute  of 
fuel  and  even  of  water,  which  could  be  utilized  for  power. 
Labor  being  exceedingly  cheap  and  cheap  transportation  not 
being  available  to  these  localities,  no  more  economic  process 
could  be  substituted. 

The  ore  is  broken  and  crushed  in  a  Chilian  mill  or  stamp 
mill,  and  then  pulverized  in  the  arrastra.  The  arrastra  con- 
sists of  a  circular,  paved  floor  over  which  a  heavy  stone  is 
dragged.  The  stone  is  attached  to  a  horizontal  beam  by  means 
of  chains  or  straps,  and  the  beam  is  carried  on  a  post  which 
revolves  about  a  pivot  in  the  center  of  the  pavement.  A  stone 
curbing  prevents  the  escape  of  material  during  the  grinding. 
In  some  arrastras  more  than  one  stone  is  attached  to  the  mov- 
ing part.  The  mill  is  driven  with  mules  or  by  water  power, 
if  available.  Water  is  added  with  the  ore  until  it  is  about  the 
consistency  of  paste,  and  if  gold  is  present,  mercury  is  added 
during  the  grinding.  When  ground  sufficiently  fine,  water  is 
added,  and  the  pulp  is  baled  out  into  reservoirs,  where  it  re- 
mains until  a  large  amount  of  the  water  has  been  evaporated 
by  the  sun's  heat.  It  is  then  taken  to  the  amalgamating  floor 
or  patio. 

The  patio  is  a  large,  paved  court  with  enough  slope  for  drain- 
age. The  ore  is  spread  on  the  patio  in  circular,  flat  heaps  call- 
ed tortas.  The  larger  heaps  are  upwards  of  I  foot  in  depth 
and  50  feet  in  diameter,  and  contain  100  tons  or  more  of  ore. 
The  heaps  are  prevented  from  further  spreading  by  means  of 
curbing.  Salt  is  shoveled  into  the  torta  and  the  treading  is  be- 


SILVER  249 

gun.  A  number  of  mules  are  driven  around  on  the  torta  for 
several  hours.  The  treading  is  resumed  next  day  with  the 
addition  of  magistral  (copper  sulphate)  and  mercury.  The 
work  is  fatiguing  to  the  animals,  and  is  injurious  to  the  feet. 
The  time  required  to  work  off  a  torta  is  from  15  days  to  more 
than  a  month,  depending  on  the  condition  of  the  ore.  Some 
ores  amalgamate  naturally  more  freely  than  others,  and  the 
rate  of  amalgamation  is  greatly  increased  by  increasing  the 
temperature  of  the  material.  The  torta  is  not  heated  artificial- 
ly except  by  the  chemical  action  of  the  substances  added. 

The  next  operation  is  the  separation  of  the  silver  amalgam 
A  quantity  of  mercury  is  generally  added  to  collect  the  hard- 
ened grains.  The  ore  with  the  amalgam  is  then  transferred  to 
settling  vats,  where  it  is  made  thin  with  water  and  stirred  to  col- 
lect the  amalgam.  The  gangue,  which  is  the  lighter  material,  is 
kept  in  suspension  and  is  drawn  off  with  the  water.  The 
amalgam  is  further  cleansed  of  heavy  particles  of  ore,  and  then 
strained  and  distilled. 

Only  about  75  per  cent,  of  the  silver  in  the  ore  is  recovered 
by  the  patio  process.  The  loss  of  mercury  is  high,  some  being 
lost  mechanically  and  some  by  the  chemical  action  of  sulphides 
and  chlorides  in  the  ore.  The  amount  of  mercury  to  be  used 
in  each  operation  is  determined  by  first  amalgamating  a  small 
amount  of  ore,  or  better,  by  first  assaying  the  ore  for  silver. 
A  loss  of  mercury  which  would  result  from  the  addition  of  an 
excess  of  the  chemicals  may  be  prevented  by  adding  lime  to 
the  torta. 

The  Washoe  Process. — This  process  is  operated  on  much  the 
same  principle  as  the  patio  process,  but  the  ore  is  treated  much 
more  rapidly  and  with  greater  economy  and  efficiency.  The 
work  is  done  almost  entirely  by  machinery,  including  the  prep- 
aration of  the  ore  and  the  final  separation  of  the  amalgam. 
The  machinery  consists  chiefly  of  rock  breakers,  stamp  mills, 
concentrators,,  amalgamating  pans  and  settlers.  The  rock 
breaker  and  stamp  mill  are  illustrated  and  described  in  Chapter 
VI.  The  ore  is  crushed  wet  and  to  such  a  degree  of  fineness 
as  will  pass  through  a  3O-mesh  sieve. 


250  METALLURGY 

The  crushed  ore  is  conveyed  by  the  stream  of  water  through 
the  mortar  sieves  into  settling  tanks.1  A  series  of  these  tanks 
is  arranged  in  front  of  the  stamps  in  sufficient  number  to  take 
the  entire  output  of  pulp.  After  rilling  two  or  three  tanks  the 
stream  of  pulp  is  turned  into  another  set,  while  the  solid  mat- 
ter in  the  first  slowly  settles.  The  water  is  drawn  off  when  it 
has  cleared  sufficiently,  and  the  pulp  is  transferred  to  the  pans 
for  fine  grinding  and  amalgamating. 

The  Amalgamating  Pan  is  of  the  construction  shown  in  Fig. 
81.  It  is  a  circular  vessel  having  an  inside  diameter  of  about 
five  feet.  The  bottom  is  of  cast  iron,  and  the  sides  are  constructed 
of  wooden  staves  held  at  the  bottom  by  the  casting  itself  and 
above  by  iron  loops.  Some  smaller  pans  are  made  entirely  of  iron. 
A  vertical  shaft,  having  its  bearings  in  a  cast  iron  cone  or 
cylinder  bolted  to  the  bottom  of  the  pan,  revolves  and  carries 
the  agitating  and  grinding  device  known  as  the  muller  around 
with  it.  The  muller  is  a  flat,  cast  iron  ring  supported  by  spread- 
ing arms  which  are  attached  to  the  upper  end  of  the  shaft.  The 
muller  is  adjustable  at  different  distances  from  the  bottom  of 
the  pan  by  means  of  the  screw  and  hand  wheels  at  the  upper 
end  of  the  shaft.  The  lower  end  of  the  vertical  shaft  carries 
a  miter  wheel  which  gears  into  a  corresponding  wheel  on  the 
horizontal  driving  shaft.  If  the  pan  is  to  be  used  for  grinding, 
the  muller  is  armed  with  adjustable  and  renewable  shoes  and 
the  bottom  of  the  pan  with  dies,  which  take  the  wear.  A 
steam  pipe  is  let  into  the  side  of  the  pan  for  introducing  steam 
to  heat  the  pulp.  Some  pans  are  provided  with  steam  jackets 
underneath.  The  pan  is  covered  and  has  an  outlet  from  the 
bottom  for  drawing  off  the  pulp. 

As  the  pulp  is  charged  into  the  pan,  water  is  supplied  from 
a  hose.  The  muller  is  raised  and  revolved  at  the  rate  of  60 
revolutions  or  more  per  minute,  and  is  lowered  as  the  ore  be- 
comes finer.  In  the  course  of  an  hour  or  two  the  ore  is  fine 
enough  for  amalgamating.  It  is  heated  and  mercury  is  added 
in  sufficient  quantity  to  alloy  with  all  the  silver  and  remain 
1  Ores  containing  sulphides  of  iron,  etc.,  or  any  which  may  be  con- 
centrated with  advantage  by  washing  are  run  over  frue  vanners  before 
settling.  See  illustration,  p.  55. 


SILVER 


251 


Fig.  81— Amalgamating  Pan.     (Allis-Chalmers  Co.) 


252  METALLURGY 

liquid.  Copper  sulphate  and  salt  are  added  either  at  the  be- 
ginning of  the  grinding  or  with  the  mercury.  The  muller  is 
raised  somewhat  when  the  mercury  is  added  to  prevent  "flour- 
ing," and  the  motion  is  maintained  for  two  hours  longer  while 
the  amalgamation  is  in  progress.  The  speed  of  the  muller  is 
checked  toward  the  end,  and  when  the  amalgamation  is  com- 
pleted the  pulp  is  drawn  off  into  the  separator. 

The  Settler  or  Separator  is  somewhat  like  the  pan  in  con- 
struction, except  that  it  is  riot  designed  for  grinding.  The  bot- 
tom, which  is  of  iron,  slopes  to  one  side  to  allow  the  mercury 
to  collect.  In  the  side  of  the  settler  and  at  different  levels  are 
holes  for  drawing  off  the  pulp.  These  are  closed  with  plugs 
when  not  in  use.  The  settler  is  placed  near  the  pan  and  on  a 
lower  level  to  facilitate  the  transfer  of  pulp. 

The  pulp  in  the  settler  is  thinned  with  water  and  is  stirred 
for  some  time  with  the  muller.  This  effects  a  separation  of 
the  heavier  particles,  which  settle  and  remain  undisturbed  on 
the  bottom,  while  the  lighter  material  is  prevented  from  settling. 
The  pulp  is  drawn  off  by  removing  the  uppermost  plug  and  the 
others  successively,  and  finally  the  amalgam  with  the  heavy 
particles  of  ore,  is  run  out  from  the  bottom.  The  pulp  carries 
some  silver  and  mercury,  and  is  treated  in  secondary  settlers 
("'agitators")  or  run  over  concentrating  tables. 

The  amalgam  is  collected  from  a  number  of  pans  and  set- 
tlers, and  is  further  cleansed  in  a  small  pan  (the  "clean  up 
pan")  with  the  addition  of  more  mercury  and  water.  The 
amalgam  is  then  strained  through  canvas  bags  and  squeezed 
to  remove  the  excess  of  mercury.  The  mercury  contains  sil- 
ver and  is  returned  to  the  pans.  The  solid  amalgam  cake  is  dis- 
tilled. 

The  Retort  for  distilling  the  mercury  is  an  iron  cylinder, 
three  to  five  feet  long  and  one  foot  in  diameter.  It  is  support- 
ed~vertically  or  horizontally  in  a  suitable  heating  furnace.  One 
end  of  the  retort  is  open  to  receive  the  charge,  and  is  closed 
during  the  distillation  by  a  close-fitting,  iron  door.  The  other 
end  communicates  with  an  iron  tube  which  carries  away  the 
mercury  vapor.  At  a  short  distance  from  the  furnace  the  tube 


SILVER  253 

is  bent  downward,  and  the  end  dips  under  water.  The  incline 
of  the  tube  is  cooled  by  passing  it  longitudinally  through  a 
larger  tube  in  which  water  is  kept  circulating.  By  this  ar- 
rangement air  is  prevented  from  entering  the  retort,  and  the 
mercury  is  condensed  and  received  in  the  basin  of  water.  The 
charge  for  a  retort  of  the  above  dimensions  is  about  1,200 
pounds  yielding  about  200  pounds  of  silver. 

The  Washoe  process  is  modified  in  different  localities  to 
suit  the  conditions.  In  this  country  the  Boss  process,  which 
is  one  of  recent  development,  has  proved  very  successful.  It 
is  a  continuous  process,  employing  a  series  of  pans  for  grind- 
ing the  pulp  from  the  stamps  and  another  series  of  amalgamat- 
ing pans  and  settlers,  doing  away  with  the  tanks.  Pan  amalga- 
mation is  also  practiced  in  connection  with  dry  crushing  and 
roasting.  The  ore  having  been  chloridized  in  the  dry  way,  is 
ground  and  amalgamated  in  pans  as  in  the  Washoe  process. 
The  yield  of  silver  may  be  as  high  as  97  per  cent.,  while  85  per 
cent,  is  considered  the  highest  yield  that  can  be  reached  with 
profit  by  the  Washoe  process. 

Barrel  Amalgamation. — The  amalgamation  of  ores  in  barrels 
was  begun  in  Europe  more  than  a  hundred  years  ago.  It  is 
still  practiced,  and  is  used  to  some  extent  in  this  country,  chiefly 
for  the  treatment' of  roasted  ore.  The  barrels  are  usually  made 
of  white  pine,  strengthened  with  iron,  and  lined  on  the  inside 
with  blocks  of  wood  placed  so  that  the  wear  is  on  the  end  of 
the  fibres.  The  barrel  is  supported  on  trunnions,  one  of  which 
is  hollow  for  the  admission  of  steam.  It  is  rotated  by  water 
or  other  power.  There  is  an  opening  in  the  side  of  the  barrel 
lor  introducing  and  withdrawing  the  charge,  the  opening  be- 
ing closed  with  a  wooden  stopper  when  not  in  use. 

A  charge  of  a  ton  of  ore,  and  usually  some  scrap  iron  in 
small  pieces  are  introduced  with  enough  water  to  make  the  mass 
flow,  and  the  barrel  is  driven  at  the  rate  of  15  revolutions  per 
minute  for  two  hours.  Mercury  is  then  added  and  the  barrel 
is  rotated  for  from  18  to  20  hours.  The  pulp  is  heated  with 
steam  to  hasten  amalgamation.  A  few  hours  after  the  opera- 
tion is  begun  the  charge  is  examined,  and  if  necessary,  water  or 


254  METALLURGY 

roasted  ore  is  added  to  bring  it  to  the  proper  consistency.  At 
the  end  of  the  operation  water  is  added  and  the  barrel  is 
turned  very  slowly  to  allow  the  mercury  to  collect.  The  main 
portion  of  the  amalgam  can  then  be  drawn  off  separately.  The 
pulp  is  received  in  a  large  agitator  in  which  any  remaining' 
amalgam  and  mercury  are  separated.  The  treatment  of  the 
amalgam  is  the  same  as  in  other  processes. 

Chemistry  of  Chloridizing  and  Amalgamating  Processes. — 
Considering  first  the  conversion  of  the  ore  by  roasting  with 
salt,  it  is  perhaps  impossible  to  properly  express  the  chemical 
changes  here  involved  by  equations.  The  reactions  probably 
differ  somewhat  between  slow  and  rapid  conversion.  If  the 
salt  is  added  after  a  preliminary  roasting,  as  is  generally  done 
in  reverberatory  furnaces,  there  are  two  distinct  stages  in  the 
conversion.  First  the  base  metals  are  converted  into  sulphates 
and  oxides,  and  the  silver  into  sulphate.  During  the  second 
stage  the  sulphates  react  with  sodium  chloride,  forming  chlorides 
of  the  respective  metals  and  sodium  sulphate.  Some  of  the 
sulphates  decompose  with  the  liberation  of  sulphur  trioxide. 
This  reacts  with  sodium  chloride,  forming  chlorine,  or  if  water 
is  present,  hydrochloric  acid.  The  chlorine  would  attack  any 
metallic  silver  with  which  it  came  in  contact.  The  chloridizing 
may  be  finished  in  the  furnace,  though  in  rapid  conversion  the 
ore  is  exposed  to  actual  furnace  heat  for  but  a  few  seconds. 
In  the  Stetefeldt  furnace  the  chloridation  of  the  ore  is  but  little 
more  than  half  completed  during  the  descent.  If  it  is  with- 
drawn and  allowed  to  cool  gradually  as  much  as  95  per  cent, 
of  the  silver  may  be  converted  into  chloride.  (Schnabel). 

The  following  are  essential  chemical  changes  occurring  dur- 
ing the  wet  chloridation  of  silver  ore: 

CuS04  -f  2NaCl  ==  Na2SO,  -f  CuCl2 
2CuCl2  +  2Hg  ==  Cu2Cl2  +  HgaCl, 
Ag2S  +  CuCl2  ==  AgCl  -f  CuS 
Ag2S  +  Cu2Cl2  >*  2AgCl  -f  Cu2S 
2AgCl  +  Hg2  ==  Hg2Cl2  +  Ag2 
4AgCl  +  Fe2  +  Hg,  =  =  Fe2Cl,  -f  Ag4HgA.. 
With  the  exception  of  the  last,  these  reactions  are  common  to 


SILVER  255 

all  amalgamating  processes.  By  the  last  reaction  it  is  seen  that 
there  is  a  saving  of  mercury  in  the  use  of  iron.  Iron  is  pur- 
posely added  in  the  barrel  process,  and  in  the  pan  process  it  is 
derived  from  the  mortars,  pans,  etc.  Egleston  has  estimated 
that  for  a  ton  of  ore  crushed  3*4  to  6^2  pounds  of  iron  are 
worn  from  the  battery  and  from  7^  to  n  pounds  from  the 
pan. 

3.  Leaching 

The  leaching  or  so  called  wet  methods  depend  upon  the 
conversion  of  the  silver,  if  necessary,  into  soluble  form,  leach- 
ing it  from  the  ore,  and  subsequently  precipitating  it  from  the 
aqueous  solution.  They  are  used  chiefly  for  ores  containing 
large  quantities  of  foreign  sulphide.  The  processes  are  com- 
monly named  after  their  inventors  or  improvers. 

Ziervogel  Process. — The  ore  is  carefully  roasted,  beginning 
with  a  low  temperature,  to  convert  the  silver  into  sulphate. 
The  roasted  ore  is  lixiviated  with  water  to  dissolve  the  sulphate, 
and  the  silver  is  precipitated  with  copper,  the  copper  being  re- 
covered by  precipitation  with  scrap  iron.  This  process  is  adapt- 
able only  to  ores  containing  iron,  copper  or  lead,  since  the 
sulphate  of  silver  can  not  be  readily  formed  directly  by  roast- 
ing. 

Augustin  Process. — The  ore  is  roasted  and  chloridized  with 
salt.  It  is  then  lixiviated  with  a  saturated  solution  of  salt 
which  slowly  dissolves  the  silver  chloride.  The  silver  is  sub- 
sequently precipitated  from  the  solution  with  copper.  The  pro- 
cess is  seldom  used. 

Patera  Process. — In  this  process  the  silver  is  chloridized  by 
roasting  with  salt,  the  chloride  is  dissolved  in  a  solution  of 
sodium  or  calcium  thiosulphate  and  silver  sulphide  is  pre- 
cipitated from  this  solution  by  adding  sodium  or  calcium  sul- 
phide. 

The  ore  is  lixiviated  in  large  wooden  vats  provided  with 
false  bottoms,  over  which  filtering  cloth  is  spread.  The  solu- 
tion is  conducted  from  the  bottom  of  the  vat  into  the  precipitat- 
ing tank  by  means  of  pipes.  If  the  ore  contains  a  large  amount 
of  foreign  matter  which  is  soluble  in  water  it  is  first  leached  in 


256  METALLURGY 


the  vat  with  cold  water.  The  thiosulphate  solution  is  run  on 
the  top  and  allowed  to  percolate  through  the  mass  of  ore  until 
the  silver  has  been  dissolved  out  as  far  as  is  practicable. 

The  precipitation  of  the  silver  sulphide  is  hastened  by  agitat- 
ing the  solution  with  wooden  stirrers  or  by  means  of  compress- 
ed air.  The  following  equations  show  the  principal  chemical 
changes  in  the  solution  and  in  the  precipitation. 

2AgCl  +  Na2S203  =  Ag2S203  -f  2NaCl 
2AgCl  +  2Na2S2O3  =  Ag2S2O3.Na2S2O3  -f  2NaCl 

Ag2SA  +  Na2S  ==  Ag2S  +  Na2S2O3 
Ag2S203.2Na2S203  -f    Na2S  -  Ag2S   -f  3Na2S2O;r 
The  strength  of  the  thiosulphate  varies  from  X  to  T/^  Per  cent, 
of  the  salt,   depending  upon  the   richness   of  the  ore.     Strong 
solutions  are  objectionable  since  they  dissolve  more  of  the  base, 
metallic  compounds  in  the  ore. 

The  precipitate  is  separated  by  filtration,  and  is  either  dried 
and  smefted,  or  dissolved  in  hot,  concentrated  sulphuric  acid, 
from  which  solution  the  silver  is  precipitated  with  copper, 
(Dewey- Walter  Process.) 

The  Russell  Process  is  a  modification  of  the  Patera  process. 
It  is  used  in  connection  with  the  latter  for  recovering  silver 
from  incompletely  roasted  ores  and  for  treating  ores  contain- 
ing galena  and  blende. 

The  ore  is  chloridized  and  leached  as  in  the  Patera  process. 
Without  removing  the  ore  from  the  vat  it  is  further  leached 
with  a  solution  of  copper-sodium  thiosulphate  which  dissolves 
the  undecomposed  silver  sulphide — 

3Ag2S  -f  2Na2S203.3Cu2S203  =  3Ag2S2O3.2Naj2S2O3  +  3Cu2S. 
The  solution  of  the  double  salt  requires  to  be  circulated  through 
the  ore  for  a  long  time  as  its  action  is  very  slow. 

With  ores  containing  galena  the  lead  is  dissolved  by  the  thio- 
sulphate solution  and  appears  with  the  silver  in  the  precipitate, 
and  subsequently  in  the  bullion.  Russell's  method  for  getting 
rid  of  the  lead  is  to  add  sodium  carbonate  to  the  thiosulphate 
solution  and  to  filter  off  the  precipitated  lead  carbonate.  This 
necessitates  the  use  of  the  sodium  salt  in  the  solution  of  the 
ore,  since  calcium  would  be  precipitated  by  sodium  carbonate. 


SILVER  257 

Zinc  is  dissolved  in  the  preliminary,  hot  water  leaching,  being- 
converted  into  sulphate  by  the  roasting. 

The  Cyanide  Process. — The  use  of  cyanides  in  the  extraction 
of  silver  is  a  recent  practice,  and  one  that  has  not,  as  yet, 
gained  much  headway.  Cyanide  of  sodium  or  potassium  may 
be  used  to  dissolve  either  metallic  silver  or  the  chloride.  A 
double  cyanide  of  silver  and  the  alkali  metal,  soluble  in  water, 
is  formed,  and  from  the  solution  the  silver  may  be  precipitated 
with  hydrochloric  acid  or  with  zinc  and  other  metals.  The 
cyanide  process  has  so  far  been  used  chiefly  for  native  silver 
ores,  carrying  gold. 

SILVER  REFINING 

The  silver  which  has  been  obtained  by  the  distillation  of 
amalgam  or  by  .  the  cupellation  of  the  lead  alloy  is  further 
purified  by  remelting  with  the  proper  fluxes  for  removing  the 
base  metals.  The  silver  is  melted  in  graphite  crucibles,  the 
crucible  being  heated  in  a  muffle  furnace.  If  base  metals  are 
present  niter  is  added  to  oxidize  them  and  the  oxides  are  dis- 
solved by  adding  borax.  If  lead  is  present  it  is  removed  by 
throwing  some  bone  ash  over  the  surface  of  the  molten  silver, 
the  lead  oxide  that  forms  being  absorbed.  The  bone  ash  with  any 
dross  is  easily  skimmed  off  without  loss  of  silver  by  first  flux- 
ing it  with  borax.  The  silver  is  not  kept  in  the  furnace  any 
longer  than  is  needed  as  there  would  be  loss  from  volatilization. 
It  is  cast  into  molds  and  kept  covered  with  charcoal  while  cool- 
ing to  prevent  the  absorption  of  oxygen.  For  the  parting  of 
silver  and  gold  see  p.  270. 


CHAPTER  XXVI 


GOLD 

Ores. — Gold  is  only  known  to  occur  native  and  in  combina- 
tion with  tellurium.  Telluride  ores  have  been  met  with  in 
various  localities,  but  they  are  rarely  of  importance.  Native 
gold  is  generally  alloyed  with  silver  and  often  occurs  with 
pyrites,  galena  and  other  sulphides.  It  also  occurs  in  oxidized 
ores,  is  often  in  quartz  and  in  other  rocks.  Gold  ores  are  either 
found  in  rock  mass  (reef  gold)  or  beds  of  earth  and  gravel 
(alluvial  gold).  Alluvial  deposits  are  commonly  called  placers. 
They  have  been  carried  down  by  water  after  the  disintegration 
of  gold-bearing  veins.  The  gold  is  generally  found  in  the 
form  of  small  grains  or  scales,  disseminated  through  the  rock 
mass  or  mingled  with  the  sands.  The  larger  pieces  sometimes 
found  are  called  nuggets. 

Gold  has  been  mined  in  almost  every  country.  The  richest 
deposits  so  far  known  are  those  of  Australia,  South  Africa 
and  North  America.  Most  of  the  gold  in  the  Western  Hemi- 
sphere has  been  found  along  the  Pacific  slope.  It  occurs  all 
the  way  from  Alaska  to  Chili,  the  richest  deposits  being  in 
Alaska  and  California. 

Properties. — Gold  is  easily  recognized  by  its  distinct  yellow 
color,  malleability  and  insolubility  in  acids.  While  of  a  yellow 

or  in  mass,  finely  divided  gold  or  gold  leaf  shows  colors  in 

nation  from  green  to  blue  and  red  by  transmitted  light.  The 
tenacity  of  gold  is  about  the  same  as  that  of  silver,  and  in  mal- 
leability and  ductility  it  exceeds  all  other  metals.  A  film  of 
gold  has  been  reduced  to  1/870,000,000  inch  in  thickness.  The 
melting  point,  as  determined  by  different  experimenters,  varies 
somewhat,  the  average  falling  a  little  below  i,ioo°C.  At  high 
temperatures  it  is  perceptibly  volatile,  the  volatility  being  in- 
creased by  the  presence  of  other  metals.  Gold  alloys  with  the 
common  metals  and  is  readily  amalgamated.  It  absorbs  various 
gases,  even  in  the  solid  state,  when  heated  to  redness.  It  is 


GOLD  259 

a  good  conductor  of  heat  and  electricity.     The  specific  gravity 
*  19-3- 

The  presence  of  but  minute  quantities  of  most  metals  renders 
gold  brittle.  The  metals  which  have  the  most  marked  effect 
upon  the  properties  of  gold  are  lead,  bismuth,  arsenic,  antimony 
and  tin.  Silver  and  copper  and  the  metals  of  the  platinum  group 
harden  gold  but  do  not  seriously  affect  its  malleability  when  al- 
loyed in  small  proportions.  Copper  is  commonly  alloyed  to 
prevent  the  rapid  wear  of  gold  in  jewelry,  coins,  etc. 

Chemical  Properties. — Two  oxides  of  gold  are  known,  but 
neither  can  be  prepared  directly  from  the  metal  and  oxygen. 
Gold  is  not  dissolved  by  any  single  acid,  but  it  is  dissolved  in 
the  presence  of  chlorine,  bromine,  thiosulphates  and  cyanides. 
Dry  chlorine  does  not  attack  gold  unless  it  be  in  the  form  of 
leaf  or  powder.  Gold  is  readily  precipitated  from  its  solutions, 
and  all  its  compounds  are  decomposed  by  heating  in  the  air. 
THE  EXTRACTION  OF  GOLD 

The  metallurgy  of  gold  is  closely  allied  to  that  of  silver.  The 
methods  for  its  extraction  might  well  be  classed  in  a  similar  way, 
an  exception  being  allowed  for  the  recovery  of  gold  by  simple 
washing. 

i.     Washing 

These  refer  to  the  recovery  of  gold  from  alluvium 
by  settling  the  gold  from  a  suspension  of  the  material 
in  water.  Such  methods  are  not  of  much  significance, 
though  they  are  widely  used  by  unp regressive  people,  and 
serve  to  some  extent  the  purposes  of  prospectors.  Mention 
only  is  made  of  the  washing  in  pans  and  by  means  of  the  cradle 
and  the  torn.  The  pan  is  usually  a  shallow,  sheet  iron  vessel 
with  a  depression  in  the  bottom  for  retaining  the  gold.  The 
pan  with  the  earth  is  held  under  running  water  and  given  a 
rotary  motion.  The  gold  settles  and  the  lighter  material  is 
carried  away  with  the  stream. 

The  cradle  is  a  trough-like  box,  mounted  on  rockers  and  in- 
clined slightly.  On  the  bottom  of  the  box  are  riffles  and  above 
the  bottom  is  a  sieve.  As  the  ore  is  thrown  on  the  sieve  with 
water  the  fine  material  is  washed  through  and  flows  down  the 
inclined  bottom.  The  earthy  matter  is  carried  over  the  riffles 


2(50  METALLURGY 

and  the  heavier  gold  particles  are  caught.     The  settling  of  the 
gold  is  aided  by  rocking  the  device. 

The  torn  works  somewhat  on  the  same  principle,  though  it 
is  of  different  construction.  It  consists  of  two  stationary,  in- 
clined troughs  so  placed  that  the  one  delivers  the  stream  into 
the  other.  The  upper  trough,  which  receives  the  ore,  is  pro- 
vided with  a  sieve  at  the  lower  end  to  prevent  gravel  from  pass- 
ing out.  Sufficient  water  is  run  into  the  upper  trough  to  sluice 
out  the  ore.  The  stream  passes  over  riffles  in  the  lower  trough 
and  deposits  a  part  of  the  gold.  The  length  of  the  torn  varies, 
being  upwards  of  30  feet. 

All  purely  washing  methods  are  wasteful,  often  recovering 
only  half  of  the  gold.  They  are  used  by  Chinese  for  working 
the  tailings  of  some  larger  operations  in  California. 

2.    Smelting 

Gold  that  is  associated  with  the  base  metals,  copper  and  lead, 
is  recovered  as  a  by-product  when  the  ores  of  these  metals  are 
smelted.  In  some  instances,  gold  ores  are  treated  by  mixing 
them  with  rich  lead  ore  and  smelting  for  work  lead. 

PROCESSES 
3.    Amalgamating 

The  treatment  of  ores  bearing  precious  metals  varies  greatly, 
owing  to  their  variation  in  value  and  in  physical  condition.  Gold 
and  silver  amalgamation  processes  are  in  many  cases  identical, 
but  the  amalgamation  of  gold  strictly  is  usually  a  less  difficult 
problem,  and  may  be  accomplished  by  simpler  means.  Gold 
ores  are  classed  as  "free  milling"  and  "refractory,"  the  former 
being  such  as  may  be  amalgamated  without  preliminary  treat- 
ment other  than  crushing.  Of  the  gold  amalgamation  processes 
the  most  important  are  those  of  Hydraulicing,  Dredging  and 
Milling. 

Hydraulicing. — This  process  comprises  both  the  mining  of 
the  ore  and  the  extraction  of  the  gold.  It  consists  in  wearing 
down  the  bank  of  ore  by  means  of  a  spray  of  water  under  power- 
ful pressure,  and  conducting  the  stream  through  sluices  to  de- 
posit the  gold.  Mercury  is  placed  in  the  bottom  of  the  sluices 
to  collect  the  gold. 

The  water  for  hydraulic  mining  is  brought  from  upper  coun- 


GOLD  26l 

try,  often  many  miles  distant,  in  conduits  or  flumes,  and  is  de- 
livered at  the  work  in  an  iron  pipe  about  30  inches  in  diameter. 
The  water  is  led  to  the  proper  position  in  smaller  pipes  which 
are  provided  with  movable  nozzles  called  "monitors"  or  "giants." 
The  direction  of  the  stream  is  determined  by  an  attendant. 

Sluices  vary  much  in  length.  The  average  is  about  1,200 
yards,  though  some  are  several  miles  in  length.  The  width  is 
3  to  6  feet  and  the  depth  about  2^  feet.  The  sluice  is 
built  of  plank  and  given  an  incline  of  about  6  inches  for  each 
32  feet,  or  more  for  sluggish  material.  The  bottom  is  paved 
with  wooden  blocks,  or  more  commonly,  with  stone.  The  spaces 
between  the  stones  are  partly  filled  with  fine  gravel  and  upon 
this  the  mercury  is  poured.  The  stream  runs  through  a  grizzly 
to  separate  boulders  which  should  not  be  carried  into  the  sluice. 

The  greater  part  of  the  gold  is  retained  in  the  first  hundred 
feet  of  the  sluice.  At  intervals  the  mercury  is  removed,  and  at 
long  intervals  the  entire  pavement  is  taken  out  and  the  mercury 
recovered.  The  amalgam  is  washed  and  the  gold  is  separated 
by  one  of  the  usual  methods. 

Hydraulic  mining  has  been  stopped  by  law  in  many  localities 
on  account  of  the  injury  to  agricultural  interests.  The  chief 
damage  has  been  due  to  the  filling  of  river  channels  with  the 
enormous  quantity  of  tailings  from  the  sluices,  resulting  in  a 
submerging  of  the  low  lands.  The  practice  has  been  followed 
chiefly  in  California. 

Dredging. — This  process,  like  hydraulicing,  is  more  of  a 
mining  than  a  metallurgical  proposition.  It  has  been  substituted 
tor  hydraulicing  in  some  localities,  being  of  more*  recent  de- 
velopment, and  is  now  managed  so  as  not  .to  seriously  injure 
agricultural  lands. 

The  dredge  is  a  huge  machine  for  raising,  concentrating  and 
amalgamating  soft  ores.  The  ore  is  raised  by  bucket  belts,  dip- 
pers or  other  means,  and  is  delivered  to  the  concentrating  and 
amalgamating  apparatus.  The  entire  machinery  is  floated  on 
a  scow,  so  that  it  is  easily  moved.  The  dredge  can  only  be 
used  on  river  bottoms  or  inland  so  far  as  it  can  dig  its  way  and 


262 


METALLURGY 


Gold  Dredge.     (New  York  Engineering  Co.) 


GOLD  263 

be  followed  by  the  water.1  It  is  useless  if  many  boulders  are 
encountered. 

Milling:. — This  has  reference  to  those  processes  in  which  the 
ore  is  crushed  before  amalgamating.  Of  the  different  mills 
employed  for  crushing  gold  ores  but  two  need  be  mentioned 
here — the  stamp  and  the  Huntington  mills. 

Stamp  mills,  designed  specially  for  crushing  gold  ores,  dif- 
fer in  but  few  details  from  those  used  for  silver  ores.  With 
free  milling  ores  amalgamated  copper  plates  are  fastened  length- 
wise and  inside  of  the  mortar,  and  the  stream  of  pulp  is  led  from 
the  mortar  over  additional  plate  surface,  and  finally  through 
sluices  or  concentrators.  A  small  amount  of  mercury  is  usual- 
ly fed  into  the  mortar.  The  plates  are  prepared  by  rubbing 
mercury  over  the  clean  surface  to  form  an  amalgam.  A  better 
amalgamating  surface  is  made  by  first  plating  the  copper  with 
silver.  The  plates  are  more  effective  after  some  gold  amalgam 
has  been  formed.  Brass  plates,  containing  60  per  cent,  of  cop- 
per and  40  per  cent,  of  zinc  (Muntz  metal),  have  been  used 
lately  with  good  results. 

The  first  plate,  which  is  necessarily  the  width  of  the  battery, 
is  called  the  ' "apron."  It  is  contracted  in  width  toward  the 
lower  end  which  is  about  15  inches  wide.  The  number  of  plates 
employed  depends  upon  the  capacity  of  the  mill  and  the  rich- 
ness of  the  ore.  The  pulp  passes  from  the  plates  into  a  sluice 
lined  with  amalgamated  plates,  and  thence  over  riffles  in  which 
mercury  is  placed.  The  plates  near  the  stamps  are  scraped  at 
least  once  a  day,  and  those  farther  down  at  longer  intervals  to 
remove  the  amalgam.  They  are  cleaned  afterwards  with 
cyanide  of  potassium  and  rubbed  with  mercury. 

The  tailings  from  the  sluices  may  be  concentrated  with  frue 
vanners  and  amalgamated  in  pans  or  by  means  of  other  amalgam- 
ating machinery.  Frue  vanners  are  also  used  for  concentrat- 
ing ores  containing  sulphides.  Concentrates  which  can  not  be 
leadily  or  profitably  amalgamated  may  be  treated  by  one  of  the 
leaching  processes. 

The  gold  amalgam,  as  obtained  above,  is  first  washed  with 

1  There  are  instances  in  which  water  is  pumped  to  higher  levels  to  float 
dredges. 


264  METALLURGY 

mercury,  and  then,  after  squeezing  out  the  excess  of  mercury, 
it  is  retorted.  The  methods  used  are  the  same  as  those  for 
treating  silver  amalgam. 

The  stamping  of  free  milling  ores  is  open  to  objections.  The 
mineral  matter  is  ground  into  the  particles  of  gold,  rendering 
them  less  readily  absorbed  by  the  mercury.  This  also  causes 
a  larger  portion  of  the  gold  to  float  instead  of  coming  in  con- 
tact with  the  copper  plates.  Furthermore  the  loss  of  mercury 
is  high,  due  to  "flouring"  and  "sickening."  By  the  former  term 
is  meant  the  loss  of  minute  globules  formed  mechanically,  and 
the  latter  term  has  reference  to  the  darkening  of  the  mercury  due 
to  a  coating  of  mineral  matter.  These  difficulties  are  overcome 
in  a  measure  by  crushing  in  roller  mills.  The  Huntington  mill  has 
given  satisfactory  results,  especially  for  the  softer  ores.  For 
the  illustration  and  description  of  this  mill  see  p.  53. 

4.    Leaching 

Plattner  Process. — The  gold  is  converted  into  a  soluble  chloride 
by  the  action  of  chlorine  in  the  presence  of  moisture.  This  is 
leached  from  the  ore  with  water,  and  the  gold  is  precipitated 
with  ferrous  sulphate,  charcoal,  hydrogen  sulphide  or  other 
agents. 

The  process  is  adaptable  to  many  ores  and  concentrates  which 
can  not  be  treated  by  an  amalgamating  process  on  account  of 
the  impurities  they  contain.  The  ore  is  commonly  calcined  or 
roasted  to  render  it  more  porous,  or  to  oxidize  sulphides, 
arsenides,  etc.,  which  cause  a  high  consumption  of  chlorine  by 
their  reaction  with  it.  Cintering  of  the  ore  is  avoided  as  par- 
ticles of  gold  would  be  enveloped  in  the  inert  mineral  matter. 
Also,  ores  containing  much  silver  are  more  difficult  to  treat, 
owing  to  the  protective  coating  of  silver  chloride  upon  the  gold. 

The  chlorine  is  either  prepared  in  a  generator  from  manganese 
dioxide,  sodium  chloride  and  sulphuric  acid,  or  in  the  same 
vessel  with  the  ore  from  chloride  of  lime  and  sulphuric  acid.  The 
former  method  is  more  common.  The  chloridizing  vat  is  gen- 
erally made  of  wood  with  a  protective  coating  of  tar.  The 
vats  hold  from  two  to  five  tons  of  ore.  Some  are  arranged  for 
agitating  the  ore  and  for  maintaining  it  under  pressure  during 


GOLD  265 

the  chloridizing.  The  action  of  the  chlorine  is  thereby  made 
more  rapid  and  more  complete.  The  moist  ore  is  subjected  to 
the  action  of  chlorine  for  about  two  days,  or  less  time  if  the  ore 
is  agitated.  The  vat  is  then  uncovered,  and  after  blowing  out 
the  excess  of  chlorine,  the  ore  is  leached  with  water  which  dis- 
solves the  chloride  of  gold.  Any  mineral  matter  which  is  car- 
ried through  is  removed  by  settling  or  by  filtration,  and  the 
solution  is  run  into  the  precipitating  tank.  The  precipitating 
agents  which  have  so  far  been  used  successfully  are  ferrous  sul- 
phate, hydrogen  sulphide  and  charcoal. 

2AuCl3  -|-  6FeS04  ==  Au2  -f  Fe2Cl6  -f-  2Fe2(SO4)3 
2AuCl3  +  3H2S  ==  Au2S3  +  6HC1. 

The  reaction  with  charcoal  is  not  understood,  though  it  is 
supposed  to  be  due  to  the  reducing  gases  it  contains.  It  is 
slower  in  its  action  than  the  other  reagents  and  does  not  pre- 
cipitate the  gold  at  all  in  the  presence  of  free  chlorine.  The 
solution  is  filtered  through  charcoal  powder  until  the  gold  is 
exhausted.  The  charcoal  is  afterwards  burnt,  and  the  gold  is 
recovered  from  the  ashes. 

Ferrous  sulphate  is  added  to  the  tank  and  thoroughly 
agitated  with  the  solution.  After  standing,  the  supernatant 
liquid  is  decanted  off  and  the  gold  residue  is  collected,  washed 
and  refined  in  crucibles.  The  liquid  which  is  drawn  off  is  al- 
lowed to  stand  for  some  time  in  a  settling  tank,  since  it  will 
throw  down  more  gold.  It  is  finally  filtered  through  sawdust  or 
sand  from  which  the  gold  is  recovered. 

The  precipitation  with  hydrogen  sulphide  is  a  more  recent 
practice,  and  is  more  rapid  than  the  other  methods.  Free 
chlorine  is  first  removed  from  the  solution  in  the  tank  by  pass- 
ing through  it  a  stream  of  sulphur  dioxide,  and  this  is  followed 
by  the  hydrogen  sulphide.  Both  reagents  are  generated  at  the 
plant  and  used  in  the  form  of  gas.  After  settling,  the  bulk 
of  the  solution  is  decanted  off,  and  the  precipitate  is  recovered 
by  filtration.  The  residue  is  dried  and  smelted. 

McArthur-Forrest  or  Cyanide  Process. — This  is  the  most 
important  of  the  leaching  processes  as  applied  to  gold  ores.  By 
the  use  of  potassium  cyanide  gold  may  be  extracted  with  profit 


266  METALLURGY 

from  ores  which  are  too  poor  for  treatment  by  other  methods. 
The  process  was  patented  in  1890  by  Me  Arthur  and  Forrest, 
who  introduced  it  into  all  the  leading  gold  producing  countries. 
It  is  most  adaptable  to  low  grade,  free  milling  ores.  Ores  in 
which  the  gold  is  in  the  form  of  coarse  grains  are  not  suitable 
for  cyanide  leaching,  since  the  gold  is  not  completely  dissolved. 
The  ore  must  be  in  a  finely  divided  state  or  in  such  a  porous 
state  as  will  permit  of  ready  absorption  of  the  solution.  Calcin- 
ing is  sometimes  resorted  to,  as  it  leaves  the  ore  more  open. 
If  the  ore  is  roasted  it  should  be  completely  oxidized,  so  as  not 
to  leave  acid  salts  which  would  react  with  the  cyanide. 

Since  the  solution  of  gold  in  potassium  cyanide  is  not  rapid, 
the  ore  is  kept  in  contact  with  the  solution  for  a  considerable 
length  of  time.  The  reaction  is  hastened  by  introducing  air 
with  the  cyanide.  Oxygen  is  essential,  as  has  been  demon- 
strated. When  the  supply  of  oxygen  has  been  exhausted  solu- 
tion of  the  gold  ceases.  According  to  Eisner  the  essentials  of 
the  reaction  are  as  follows: 

4Au  +  8KCN  +  2H20  +  20  ==  4KAu(CN)2  +  4KOH. 

Chemical  oxidizing  agents  such  as  the  chlorates,  peroxides 
and  the  halogens  may  be  used  with  good  effect. 

The  ore  is  usually  leached  in  a  large,  shallow  vat1  of  wood 
or  metal  properly  protected  with  paint.  The  ore  is  supported  on 
a  false  bottom,  and  the  solution  is  drawn  from  the  bottom  of 
the  vat  through  an  iron  pipe.  If  the  ore  contains  sulphates  or 
other  salts  which  would  react  with  the  cyanide  it  is  washed 
with  water,  and  any  remaining  acid  may  be  neutralized  with 
an  alkali.  The  cyanide  solution  is  let  in  from  the  bottom,  as  in 
working  upward  there  is  less  tendency  toward  the  formation 
of  channels  in  the  mass.  After  standing  for  some  time  at 
several  inches  above  the  surface  of  the  ore,  the  solution  is 
partially  drawn  off  and  more  is  run  on.  This  is  done  to  in- 
troduce air  into  the  stock.  After  the  preliminary  washing, 
the  ore  is  commonly  leached,  first  with  a  strong  solution  (0.3 
to  0.6  per  cent.),  and  after  drawing  this  off,  with  a  weak  solu- 
tion (o.i  to  0.3  per  cent).  The  ore  is  finally  washed  with 
1  Ores  can  not  be  leached  so  successfully  in  deep  vessels. 


GOU3  267 

water,  and  the  washings  are  generally  used  for  the  preliminary 
leaching  or  washing  of  a  fresh  charge. 

The  time  required  and  the  strength  of 'the  solution  varies 
much  with  different  ores.  Naturally,  the  solution  proceeds 
more  slowly  with  weak  than  with  strong  solutions,  but  there 
is  a  tendency  towards  weakening  the  solvent  on  the  part  of 
operators,  because  less  mineral  matter  is  dissolved  and  the 
cyanide  is  economized.  Sand  is  sometimes  mixed  with  very 
fine  ore  to  hasten  the  percolation. 

Precipitation  of  the  Gold. — This  part  of  the  cyanide  process 
has  received  most  attention,  as  it  has  offered  the  most  dif- 
ficulties. Many  of  the  methods  offered  are  all  right  in  theory, 
but  in  practice  have  proved  too  expensive  or  have  failed  to 
completely  precipitate  the  gold  from  the  solutions. 

The  most  common  method  of  precipitating  gold  is  with  zinc 
in  the  form  of  thin  shavings.  The  shavings  are  cut  on  a  lathe 


Fig.  84. 

from  the  edges  of  plates  of  zinc,  which  are  held  together  while 
being  turned.  The  shavings  are  supported  on  wire  screens  in 
compartment  boxes  as  shown  in  Fig.  84.  The  boxes  are  made 
of  wood  and  painted  on  the  inside  with  paraffine.  The  solu- 
tion is  supplied  through  the  pipe  shown  at  the  left.  It  passes 
under  the  first  partition  and  overflows  the  next,  and  so  on, 
rising  through  each  compartment  in  which  the  shavings  are 
contained.  The  spent  solution  is  carried  away  through  the 
overflow  pipe  shown  at  the  right.  For  drawing  off  the  pre- 
cipitate and  cleaning  up,  each  compartment  is  provided  with  a 
drain  pipe  in  the  bottom. 

The  gold  is  precipitated  in  the  form  of  a  black  powder 
adherent  to  the  zinc.  This  falls  down  to  the  bottom  of  the 
boxes  with  particles  of  zinc  as  slime. 

There  is  some  doubt  as  to  the  changes  involved  in  the  pre- 


268  METALLURGY 

cipitation  of  gold,  though  it  is  supposed  to  be  electrolytic. 
That  it  is  not  simply  a  substitution  of  zinc  for  gold  is  shown 
by  the  fact  that  the  weight  of  zinc  dissolved  is  not  a  chemical 
equivalent  of  the  gold  precipitated.  The  substitution  would  be 
as  follows : 

2AuK(CN)2  +  Zn  ==  K2Zn(CN)4  +  2Au. 

In  practice  about  12  ounces  of  zinc  are  required  for  I  ounce 
of  gold  deposited.  The  gold  is  never  recovered  completely 
though  as  little  as  four  per  cent,  has  been  left  in  the  solution. 
Impurities  affect  the  precipitation,  and  when  the  solutions  be- 
come heavily  charged  they  are  purified  or  rejected.  Copper 
in  the  solution  is  deposited  upon  the  zinc,  retarding  the  deposi- 
tion of  gold.  Since  strong  solutions  react  with  the  zinc  more 
rapidly  than  weak  ones  do,  cyanide  is  sometimes  added  to  the 
solution  as  it  comes  from  the  leaching  vat.  It  is  essential  that 
the  zinc  be  in  finely  divided  form,  hence  the  use  of  thin  shav- 
ings. Furthermore,  the  action  is  not  rapid  until  the  surface 
of  the  zinc  has  become  etched  by  the  solution. 

As  a  substitute  for  shavings,  zinc  dust  (the  by-product  of 
zinc  distillation)  is  used  at  some  plants.  The  zinc  dust  is  stir- 
red into  the  solution,  and  the  gold  precipitate  is  collected  by 
filtration.  Precipitation  by  this  method  is  very  rapid. 

Another  substitute  for  zinc  shavings  is  the  zinc-lead  couple, 
prepared  by  immersing  the  shavings  in  a  dilute  solution  of  lead, 
acetate.  The  lead-coated  shavings  are  transferred  immediately 
after  preparation  to  the  gold  solution.  This  method  has  th-^ 
advantage  of  being  very  rapid  and  of  not  precipitating  copper. 
The  gold  residue  contains  a  large  amount  of  lead,  which  is 
objectionable. 

Electricity  in  the  Cyanide  Process. — Electrolytic  methods  are 
of  later  origin,  but  they  are  being  used  quite  successfully.  Two 
processes  will  be  noted. 

The  Siemens-Halske  process,  which  has  been  used  chiefly  in 
South  Africa  is  applied  solely  to  the  treatment  of  the  gold 
solution.  The  ore  is  leached  as  in  the  ordinary  cyanide  pro- 
cess, and  the  solution  is  electrolyzed  in  wooden  boxes  18  feet 
long,  7  feet  wide  and  3  feet  deep.  In  these  are  sus- 


GOLD  269 

pended  89  sheet  iron  anodes  and  88  cathodes  of  sheet  lead. 
As  the  solution  is  circulated  through  the  boxes  it  is  subjected 
to  the  action  of  the  current,  and  the  gold  is  deposited  upon  the 
lead.  The  anodes  are  enclosed  in  canvas  to  hold  the  compounds 
that  are  formed  by  the  action  of  the  cyanide  on  the  iron. 

In  the  Felatan-Clerici  process,  developed  in  this  country,  the 
solution  is  electrolyzed  while  it  is  in  contact  with  the  ore.  The 
process  is  therefore  a  single  operation.  The  ore  is  mixed  in 
the  vat  with  enough  water  to  make  it  quite  liquid,  and  it  is 
stirred  while  solution  and  precipitation  are  in  progress.  A 
rotating  agitator  is  employed,  to  the  arms  of  which  the  iron 
anode  plates  are  attached.  The  cathode  is  a  circular  plate  of 
copper,  covered  with  mercury,  and  it  is  supported  horizontally 
a  few  inches  below  the  anode.  Besides  the  cyanide  certain 
chemicals  are.  added  to  aid  in  the  solution.  About  three  tons 
of  ore  are  treated  at  once,  and  the  precipitation  proceeds  very 
rapidly.  The  gold  and  silver  are  deposited  as  amalgams.  The 
exhausted  material  is  drawn  from  the  bottom  of  the  vat  and 
run  into  a  settler  from  which  the  solution  is  recovered. 

Explanations  of  the  electrochemical  changes  of  the  cyanide 
process  are  largely  conjectural.  Potassium  cyanide  in  solution 
i.<  decomposed  into  cyanogen  and  potassium,  and  water  into 
hydrogen  and  oxygen.  Potassium  and  water  combine  to  form 
caustic  potash,  with  the  liberation  of  hydrogen,  while  hydrogen 
and  cyanogen  from  hydrocyanic  acid.  The  double  cyanide  of 
gold  and  potassium  is  split  up  into  cyanide  of  gold  and  potas- 
sium hydroxide,  and  gold  is  precipitated,  probably  by  the  action 
of  hydrogen — 

2Au(CN)2  +  4H  ==  2Au  +  4HCN. 

Potassium  cyanide  may  be  regenerated  by  the  reaction  of  hy- 
drocyanic acid  and  potassium  hydroxide.  According  to  the 
theory  of  electrolysis  the  gold  is  dissolved  only  at  the  anode, 
though  solution  may  take  place  away  from  the  anode  by  inde- 
pendent chemical  action.  The  fact  that  oxygen  is  liberated  at 
the  anode  gives  ground  for  the  view  that  chemical  action  is 
assisted  by  the  current,  thus: 

4KCN  +  2Au  +  O  -f  H20  ==  2AuK(CN)2  +  2KOH. 


270  METALLURGY 

The  solution  of  the  gold  is  much  more  rapid  in  the  electro- 
cyanide  process  than  by  the  action  of  cyanide  alone. 

The  chief  advantages  of  the  electrolytic  methods  are  that 
time  and  labor  are  saved,  the  cyanide  is  economized  and  zinc  is 
dispensed  with  entirely.  The  gold  residue  is  much  cleaner  than 
that  obtained  by  zinc. 

Among  the  various  other  substances  that  have  been  used  to 
precipitate  gold  from  cyanide  solutions  are  zinc  amalgam, 
.aluminum,  charcoal  and  cuprous  salts. 

Treatment  of  the  Auriferous  Residues. — Gold  that  is  de- 
posited upon  zinc  is  removed,  as  far  as  possible,  by  shaking  the 
.shavings  in  water  and  sifting.  The  residue  is  dried  and 
smelted,  or  first  treated  with  dilute  sulphuric  acid  to  dissolve 
the  zinc  and  other  impurities.  It  is  then  washed  with  hot 
water,  and  after  decanting  the  washings,  the  remaining  liquid 
is  separated  by  filtration,  and  the  residue  is  melted  for  bullion. 

THE  REFINING  OF  GOLD 

The  purification  of  gold  involves  the  separation  of  base  im- 
purities, and  desilverization.  The  latter  process  is  called  part- 
ing. In  rarer  instances  the  metals  of  the  platinum  group  are  to 
be  separated.  The  base  metals  are  usually  almost  completely 
removed  before  parting.  This  is  done  by  fusing  the  gold  in 
crucibles  with  borax,  niter,  sulphur,  or  whatever  chemical  sub- 
stance is  needed  to  combine  with  and  flux  the  metals  present. 
Alloys  rich  in  copper  are  fused  with  sulphur,  whereby  the  cop- 
per is  separated  as  cuprous  sulphide  (Roessler's  method).  The 
parting  of  gold  and  silver  may  be  effected  in  many  ways.  The 
more  important  only  need  be  noted  here. 

By  Chlorine. — The  alloy  is  melted  in  a  clay  crucible  with  a 
small  quantity  of  borax.  Dry  chlorine  gas  is  passed  through 
the  charge  by  means  of  a  clay  pipe  until  the  silver  and  any  base 
metals  are  converted  into  chlorides.  Gold  may  be  rendered 
almost  absolutely  pure  in  this  way,  but  the  method  is  expensive. 

By  Sulphuric  Acid. — This  is  one  of  the  cheapest  and  most 
common  methods  of  parting.  Gold-silver  alloys  are  either 
mixed  or  more  silver  is  added  to  an  alloy  until  the  mixture  has 
.the  proper  proportion  of  the  two  metals  for  the  action  of  the 


GOLD  271 

acid.  Adding  the  silver  is  termed  inquartation.  The  alloy  is 
then  converted  into  a  thin  slab  or  granulated  by  pouring  it 
from  the  crucible  into  cold  water.  This  is  done  to  bring  a  large 
surface  area  in  contact  with  the  acid.  The  silver  is  dissolved 
by  digesting  the  granules  in  an  iron  pot  with  hot  sulphuric  acid. 
The  solution  is  drawn  off  and  the  gold  is  treated  repeatedly 
with  hot,  concentrated  sulphuric  acid.  Further  purification 
may  be  effected  by  fusing  potassium  bisulphate  with  the  gold 
and  leaching  out  the  silver  sulphate  with  water.  The  parting 
may  also  be  done  with  nitric  acid^  but  this  is  not  much  used 
now.  "?  ?  ?  ?  ?  I  &Jk  >*^  /tcJUt^er-/ 

By  Aqua  Regia. — The  highest  degree  t>f  purity  is  obtained  by 
Roessler's  method^  which  consists  in  dissolving  the  otherwise 
partially  purified  gold  with  aqua  regia.  The  silver  is  converted 
into  insoluble  chloride,  and  the  gold  is  precipitated  from  the 
solution  with  ferrous  sulphate.  The  gold  may  be  999  9/1000 
pure, 

By  Electrolysis. — This  method  is  of  comparatively  recent 
origin,  and  is  quite  extensively  used  by  refiners.  The  electrolyte 
is  a  dilute,  acidified  solution  of  silver  nitrate.  The  anodes  are 
cast  from  the  alloy  to  be  refined  and  the  cathodes  are  of  rolled 
silver.  A  dense  current  is  employed,  which  precipitates  the 
silver  free  from  gold,  while  the  gold  slimes  contain  but  very 
little  silver.  Ihe  anodes  are  enclosed  in  cloth  bags  which  re- 
tain the  gold.  Automatic  scrapers  are  employed  to  prevent  the 
growth  of  silver  crystals  from  causing  short  circuits.  The  sil- 
ver is  sufficiently  pure  for  the  market,  and  the  gold  is  purified 
to  999/IOOO  by  boiling  with  acids. 


CHAPTER  XXVII 


NICKEL,  ALUMINUM,  MANGANESE  AND  RARER  METALS 


NICKEL 

Ores. — 'Nickel  occurs  chiefly  as  silicate,  sulphide,  and 
arsenide.  The  principal  ores  are  Garnierite,  occurring  in  silici- 
ous  rocks,  and  magnetic  pyrites.  The  ore  usually  contains 
more  iron  or  copper  than  nickel,  but  the  nickel  represents  the 
main  value  in  most  cases.  Arsenic  is  also  frequently  found 
Tnth  nickel  and  also  small  quantities  of  antimony  and  chromium. 
The  amount  of  nickel  in  different  ores  is  exceedingly  variable, 
ranging  from  less  than  I  to  more  than  50  per  cent.  The 
largest  known  deposits  are  in  New  Caledonia  and  Sudbury, 
Canada.  The  metal  nickel  was  first  recognized  by  Cronstedt, 
,about  1751  (Hadfield). 

Properties.— Nickel  is  of  a  slight  grayish-white  color  and 
highly  lustrous.  It  is  exceedingly  tenacious  and  tough,  and 
is  both  malleable  and  ductile.  It  is  harder  than  iron  or  copper 
and  in  malleability  it  is  inferior  to  these  metals.  The  melting 
point  is  i, 600°  C.  Nickel  alloys  readily  with  most  metals  and  it- 
may  be  welded  to  itself  and  to  iron.  When  in  the  molten  con- 
dition nickel  occludes  carbon  monoxide  and  other  gases.  In 
conductivity  it  ranks  next  to  zinc.  It  is  slightly  magnetic. 

In  both  its  physical  and  chemical  properties  nickel  appears 
to  be  intermediate  between  iron  and  copper.  It  is  unchanged 
in  either  dry  or  moist  air  at  ordinary  temperatures.  It  is 
readily  dissolved  by  nitric  and  slowly  by  hydrochloric  and  sul- 
phuric acids.  There  are  two  oxides  of  nickel  of  which  the 
monoxide  (NiO)  is  the  more  important.  This  may  be  formed 
directly  by  heating  metallic  nickel,  or  by  heating  either  the 
sulphide  or  the  arsenide  in  an  oxidizing  atmosphere.  Both  the 
oxides  are  reducible  by  carbon  at  a  temperature  below  the  melt- 
ing point  of  nickel.  With  silica  nickelous  oxide  forms  a 
fusible  silicate.  Nickel  sulphide  occurs  naturally  and  it  may 


NICKEX,    ALUMINUM,    MANGANESE,    ETC.  273 

be  prepared  by  heating  nickel  with  sulphur  or  certain  other 
sulphides,  and  by  reducing  the  sulphate  with  carbon.  It  may 
be  decomposed  by  heating  with  it  metallic  copper,  the  products 
being  nickel  and  cuprous  sulphides.  By  melting  together  the 
sulphides  of  nickel,  copper  and  iron  with  sodium  sulphate  or 
sulphide,  the  copper  and  iron  sulphides  form  a  readily  fusible 
mixture  with  the  alkaline  salt,  while  the  nickel  sulphide  is 
fused  with  more  difficulty.  In  consequence  of  this  the  copper 
matte  separates  more  or  less  completely  from  the  heavier  nickel 
matte.  By  roasting  these  sulphides  with  salt  the  copper  may- 
be chloridized  and  the  nickel  with  the  iron  converted  into  oxide. 
Nickel  combines  readily  with  arsenic.  The  artificially  concen- 
trated arsenide  is  known  as  nickel  speiss. 

Extraction  of  Nickel. — A  number  of  methods  have  been  pro- 
posed for  the  recovery  of  nickel  from  its  ores  and  furnace 
products.  These  fall  under  the  general  heads  of  smelting,  wet 
and  electrolytic  methods.  The  general  run  of  nickel  ores  yield 
most  readily  to  smelting,  though  the  other  methods  have  been 
practiced  quite  successfully.  The  usual  smelting  process  con- 
sists in  concentrating  the  nickel  into  a  matte  or  a  speiss  by 
roasting  and  fusing,  then  roasting  the  concentrate  to  free  it 
from  sulphur  or  arsenic,  and  finally  reducing  the  nickel  with 
carbon.  The  character  of  the  ore  of  course  largely  determines 
the  method  of  treatment.  In  most  ores  the  content  of  nickel 
is  very  small,  often  below  five  per  cent.  Iron  and  usually  cop- 
per are  present  in  sulphide  ores,  and  in  silicious  ores  an  over- 
whelming mass  of  silica  must  be  dealt  with.  The  metallurgy 
of  nickel  is  often  associated  with  that  of  other  metals,  and  the 
operations  pending  its  final  isolation  may  be  long  and  tedious. 

The  ore  is  roasted  in  a  reverberatory  furnace  to  expel  the 
excess  of  sulphur,  leaving  enough  to  form  the  matte.  If  cop- 
per is  not  present  the  iron  is  fluxed  with  silica  and  the  nickel 
matte  separates.  The  smelting  of  the  matte  may  be  conducted  in 
a  reverberatory  furnace,  hearth  or  Bessemer  converter,  the  sil- 
ica being  supplied  from  the  ore  itself  or  from  the  lining  of  the 
furnace.  If  copper  is  present  the  treatment  thus  far  is  similar. 
But  the  matte  contains,  beside  the  nickel,  most  of  the  copper  and 


274  METALLURGY 

some  iron.  The  bulk  of  the  iron  is  separated  by  an  oxidizing 
fusion  with  a*silicious  flux.  The  residue  is  then  fused  with  an 
alkaline  salt  such  as  soda  ash  or  salt  cake,  which  serves  to  dis- 
solve or  absorb  the  sulphides  of  copper  and  iron.  The  nickel 
sulphide,  being  heavier,  settles  to  a  lower  level,  and  the  two 
masses  may  be  separately  tapped.  The  concentrated  nickel 
matte  is  roasted  in  a  reverberatory  furnace.  The  product  is 
nickel  oxide,  since  the  oxide  and  sulphide  of  nickel  do  not 
react  to  liberate  the  metal  as  the  corresponding  compounds  of 
copper  do.  The  oxide  is  charged  into  crucibles  or  muffles  with 
carbon  and  smelted  for  nickel. 

Oxidized  or  silicious  ores  are  sometimes  smelted  directly  in 
blast  furnaces  with  coke  to  produce  an  alloy  of  nickel  and  iron. 
A  process  has  also  been  in  use  for  making  nickel  steel,  in  which 
the  nickel  ore  is  charged  with  the  iron  into  an  open  hearth  fur- 
nace. 

Wet  and  electrolytic  processes  are  also  in  use  for  the  extrac- 
tion of  nickel.  These,  though  rarely  ever  adaptable  to  raw 
ores,  on  account  of  the  impurities  and  the  low  content  of  nickel, 
have  had  considerable  application  in  working  up  nickel-bear- 
ing products.  Wet  methods  usually  look  to  the  solution  of 
the  nickel  in  hydrochloric  or  sulphuric  acid,  its  subsequent 
precipitation  and  final  smelting.  Having  obtained  the  solution, 
the  metals  of  the  copper  group  may  be  separated  by  means  of 
hydrogen  sulphide.  Iron  may  then  be  separated  by  oxidizing 
the  solution  and  adding  calcium  carbonate.  This  also  throws 
down  any  arsenic.  The  nickel  is  recovered  from  the  solution 
by  crystallizing  it  as  the  sulphate,  or  by  precipitation  with  cal- 
cium hydroxide  or  soda. 

Electrolytic  methods  have  been  successfully  used  for  ex- 
tracting nickel,  especially  from  alloys  or  mattes  containing1  cop- 
per. Ulke  has  described  a  process  for  treating  a  matte  con- 
taining about  40  per  cent,  each  of  nickel  and  copper.  The 
matte  is  cast  directly  into  anodes,  and  the  electrolyte  is  an 
acid  solution  of  nickel  sulphate.  The  cathodes  are  of  sheet 
copper.  Upon  these  the  copper  is  deposited  from  the  solution 
as  the  anodes  are  dissolved.  The  nickel  su!phate  is  recovered 


NICKEL,    ALUMINUM,    MANGANESE,    ETC.  2/5 

from  the  solution  by  crystallization  when  it  has  accumulated  in 
sufficient  quantity;  or  instead,  it  may  be  precipitated  as  above 
or  by  electrolysis.  If  electrolysis  is  adopted  the  solution  is 
rendered  slightly  ammoniacal,  and  anodes  of  carbon  or  lead  are 
introduced.  The  nickel  is  deposited  upon  cathodes  of  sheet 
nickel. 

Nickel,  as  it  comes  from  the  smelter  is  never  pure.  One 
of  the  more  usual  methods  of  refining  consists  in  fusing  it  in 
crucibles  and  adding  magnesium.  This  reduces  any  oxides 
present,  the  magnesium  burning  away  or  entering  a  slag. 
Manganese  is  employed  to  remove  sulphur  from  nickel. 

Cobalt  is  often  associated  with  nickel,  and  it  is  recovered  by 
similar  methods.  It  somewhat  resembles  nickel  in  its  properties, 
and  though  comparatively  rare  its  use  is  becoming  extended. 

ALUMINUM 

History. — The  existence  of  aluminum  was  suspected  some 
time  before  it  was  actually  discovered.  Davy,  in  1807,  pre- 
pared aluminum  chloride,  and  then  attempted  to  isolate  the 
metal,  with  the  aid  of  electricity,  having  already  succeeded  in 
separating  the  alkali  metals  in  this  way.  Though  this  experi- 
ment was  not  successful,  it  is  an  interesting  fact  that  electrical 
methods  are  now  used  exclusively  in  the  manufacture  of 
aluminum  for  the  market,  yet  in  the  meantime  it  was  manu- 
factured by  purely  chemical  processes.  It  is  believed  that 
Oersted  succeeded  in  preparing  aluminum  amalgam,  in  1824. 
His  experiment  consisted  in  heating  aluminum  chloride  with 
potassium  amalgam.  This  lead  to  Wohler's  experiment  (1827) 
in  which  he  decomposed  anhydrous  aluminum  chloride  with 
potassium  and  obtained  small  globules  of  aluminum.  The  same 
principle  was  made  use  of  by  Deville,  Percy  and  others  who 
developed  processes  for  manufacturing  aluminum.  The  fluoride 
of  aluminum  was  substituted  for  the  chloride  and  sodium  was 
used  instead  of  potassium,  as  it  was  cheaper.  The  manufactur- 
ing cost  was  greatly  lessened  by  Castner,  who  cheapened  and 
improved  the  processes  for  making  aluminum  chloride  and 
sodium.  The  isolation  of  aluminum  by  electrolysis  was  ac- 


276  METALLURGY 

complished  in  1854  by  Bunsen  and  Deville,  who  worked  in- 
dependently of  each  other.  They  used  the  double  chloride  •  : 
aluminum  and  sodium,  which  they  electrolyzed  while  in  a  fiu:~  ! 
condition. 

Ores. — Though  the  most  abundant  metal  in  nature,  the 
materials  from  which  aluminum  can  be  economically  prepared 
are  at  present  limited.  The  only  ores  of  importance  are  Bauxite 
and  Cryolite.  The  former  is  a  mixture  of  the  hydrated  oxides 
of  iron  and  aluminum  and  the  latter  is  the  double  fluoride  of 
sodium  and  aluminum. 

Properties. — Aluminum  has  almost  the  whiteness  of  silver, 
though  a  slight  tinge  of  blue  is  generally  present,  due  to  im- 
purity or  to  forging.  The  tensile  strength  of  cast  aluminum 
is  17,042  pounds  per  square  inch,  elongation  three  per  cent. 
The  tenacity  is  improved  by  working.  The  pulling  strength  of  a 
wire  which  was  warmed  was  35,500  pounds  (Schnabel).  Alumi- 
num can  be  worked  cold,  its  best  forging  temperature  being 
about  200°  C.  It  becomes  brittle  at  higher  temperatures  and 
melts  at  625°C.  (Le  Chatelier).  It  is  volatile  at  still  higher 
temperatures.  Aluminum  alloys  with  most  metals.  The  specific 
gravity  is  2.58. 

Aluminum  is  not  oxidized  in  either  dry  or  moist  air  at 
ordinary  temperatures.  At  high  temperatures  it  becomes  coated 
with  oxide,  and  if  the  finely  divided  metal  is  kindled  it  burns 
with  great  brilliancy.  Under  such  conditions  if  it  be  in  con- 
tact with  certain  metallic  oxides  such  as  those  of  iron,  manganese, 
copper,  lead  and  chromium,  the  aluminum  is  converted  into 
alumina  and  the  other  metal  is  reduced.  The, oxide  of  alumi- 
num is  not  reduced  by  carbon  except  in  the  electric  furnace. 
Aluminum  is  not  precipitated  from  any  aqueous  solution  by  any 
metal  or  by  the  electric  current. 

Aluminum  Smelting. — Since  the  development  of  electric 
processes  the  reduction  of  aluminum  by  sodium  has  been 
abandoned.  Two  processes  have  been  used  in  this  country  for 
the  production  of  aluminum  on  the  large  scale — The  Cowles- 
Brothers'  process  and  the  Hall  process.  The  Cowles  Brothers' 
process  was  patented  in  1885,  and  their  first  plant  was  put  into- 


NICKEL,    ALUMINUM,    MANGANESE,    ETC.  277 

operation  in  Cleveland,  Ohio.  The  process  consists  in  reducing 
aluminum  from  the  oxide  in  the  presence  of  another  metal, 
which  metal  absorbs  the  aluminum  at  the  moment  of  its  libera- 
tion. The  product  is  therefore  an  alloy.  The  original  furnace 
is  a  rectangular  box  lined  with  fire-clay,  through  the  opposite 
sides  of  which  the  current  is  conducted.  Into  this  a  mixture 
of  alumina  and  charcoal  with  the  alloying  metal  is  charged. 
The  conductors  for  the  current  terminate  in  bundles  of  carbon 
sticks,  which  are  placed  near  each  other  and  imbedded  in  the 
charge.  A  powerful  current  being  turned  on,  the  carbons  first 
become  heated  and  then  heat  is  generated  in  the  mixture,  due 
to  the  resistance.  Reduction  and  fusion  follow,  carbon 
monoxide  being  liberated.  The  alloy  is  tapped  from  the  fur- 
nace, and  more  aluminum  or  more  of  the  other  metal  is  added  to 
bring  it  to  the  composition  desired.  The  extent  to  which 
electrolysis  takes  place  in  this  process  is  not  known,  but  the 
reduction  is  supposed  to  be  almost  entirely  chemical. 


Fig.  85. 

In  the  Hall  process  aluminum  is  reduced  from  alumina  in  a 
molten  bath  of  cryolite,  and  deposited  by  electrolysis.  The 
alumina  is  dissolved  in  the  cryolite,  salts  of  the  alkalies  being 
added  to  make  the  bath  more  liquid.  The  furnace  used  is  of 
the  crucible  form,  and  the  heat  is  generated  by  the 
electric  resistance  in  the  bath.  The  anodes,  which  dip  into  the 
bath  from  above,  are  of  specially  prepared  carbon,  and  the 
crucible  itself  is  the  cathode.  The  carbon  from  the  anodes 
combines  with  the  oxygen  from  the  alumina,  the  weight  of 
carbon  consumed  being  about  equal  to  the  weight  of  aluminum 
deposited.  The  Hall  process  is  used  by  the  Aluminum  Com- 
pany of  America,1  and  it  has  been  introduced  into  Europe. 
1  Formerly  the  Pittsburg  Reduction  Company. 


278  METALLURGY 

Fig.  85  shows  the  arrangement  of  an  aluminum  reduction 
furnace.  It  consists  of  an  iron  box  lined  with  graphite,  form- 
ing the  cathode,  and  graphite  anodes  supported  on  a  metal 
conductor  as  shown.  The  wires,  marked  +  and  —  show  the 
connections  for  the  current. 

The  cryolite  is  melted  in  the  crucible  and  the  alumina  is 
added  as  the  bath  becomes  impoverished.  The  aluminum  is 
deposited  on  the  bottom  of  the  crucible. 

MANGANESE 

Manganese  was  discovered  in  1774  by  Scheele,  a  Swedish 
chemist.  It  was  not,  however,  until  the  early  part  of  last 
century  that  much  attention  was  called  to  manganese.  Heath 
appears  to  have  first  manufactured  manganese  for  the  purpose 
of  alloying  it  with  iron,  and  to  appreciate  in  a  scientific  way  its 
•value  in  steel  making.  It  was  not,  however,  until  after  the  in- 
troduction of  the  Bessemer  process  for  making  steel  that  the 
manufacture  of  manganese  on  the  large  scale  was  begun. 

Ores. — The  only  ores  of  manganese  of  importance  are  the 
oxides.  These  are  known  as  Pyrolusite  (MnO2),  which  is  also 
called  black  oxide  of  manganese,  and  Hausmanite  (2MnO-|- 
MnO2).  Manganese  ores  are  widely  distributed  though  not 
abundant.  They  are  mined  in  the  Eastern  states  and  in  Canada. 
The  main  supply  to  this  country  comes  from  Brazil  and  Cuba. 

Properties. — Manganese  has  a  light-gray  color,  and  the 
fracture  shows  a  fine  granular  structure.  It  is  hard  and  brittle 
and  can  not  be  forged.  It  fuses  at  about  1,90x3°  C.  and 
alloys  readily  with  most  metals. 

Manganese  has  strong  affinity  for  oxygen  and  sulphur,  with 
which  elements  it  combines  in  different  proportions.  Manganous 
oxide  forms  silicates  analogous  to  the  silicates  of  iron.  The 
oxides  of  manganese  are  reduced  by  carbon  at  high  tempera- 
tures. 

Smelting. — Since  the  ores  of  manganese  always  carry  iron 
and  the  separation  of  the  two  oxides  is  not  practicable,  both 
metals  are  reduced  during  the  smelting  and  the  product  is  a 
ferro-alloy.  That  which  is  manufactured  to  contain  up  to  30 
per  cent,  of  manganese  is  known  commercially  as  spiegel-eisen, 


NICKEL,    ALUMINUM,    MANGANESE,    ETC.  279 

and  the  higher  grades  are  ferro-manganese.  The  latter  may 
run  as  high  as  87  per  cent,  or  even  higher  in  manganese.  In 
addition  to  the  iron,  manganese  alloys  carry  carbon,  silicon  and 
ether  impurities  absorbed  during  the  smelting. 

Manganese  ore  is  now  regularly  smelted  in  coke  blast  fur- 
naces, and  these  are  operated  essentially  in  the  same  way  as  in 
iron  smelting.  A  higher  temperature  is  required  for  the  re- 
duction of  manganese,  and  a  much  larger  percentage  of  coke 
is  used  in  the  burden.  The  slag  is  more  basic. 

Ferro-manganese  is  now  manufactured  in  the  Pittsburg 
District  and  in  most  every  large  steel  center.  At  Bethlehem 
and  Palmerton  the  New  Jersey  Zinc  Company  operate  blast 
furnaces  producing  Spiegel.  The  residues  obtained  after  smelt- 
ing Franklinite  ore  for  zinc  are  smelted  for  the  iron  and  man- 
ganese they  contain. 

RARER  METALS 

The  metals  noted  below  are  not  in  all  instances  rare  as  to 
their  occurrence,  but  their  present  applications  are  so  limited 
as  to  warrant  but  little  space  in  this  treatise. 

Chromium. — This  metal  occurs  as  the  oxide  (Chromite), 
mention  of  which  is  made  under  the  head  of  Refractory  Ma- 
terials. It  is  met  with  in  the  Eastern  states  and  California.  The 
most  important  deposits  are  in  Asia  Minor,  Greece,  Silesia 
and  New  Caledonia.  Chromium  was  discovered  by  Vauquelin, 
of  France,  in  1797. 

Chromium  may  be  prepared  by  electrolysis  of  the  chloride  in 
aqueous  solution,  by  reduction  in  a  crucible  with  aluminum  or 
carbon  and  in  other  ways.  I.t  is  usually  manufactured  for  the 
market  as  ferro-chrome  by  smelting  the  iron-bearing  ores  in 
electric  furnaces.  •  Alloys  containing  upwards  of  40  per  cent,  of 
chromium  may  be  made  in  a  blast  furnace.  The  richer  alloys 
may  be  prepared  in  crucibles,  by  reduction  with  carbon  or 
aluminum. 

Tungsten. — This  metal  occurs  as  the  oxide  in  the  mineral 
Wolframite,  being  associated  with  other  metals  (CaWO4, 
FeWO4  and  MnWO4).  It  is  also  found  in  tin  ores.  Tungsten 


28O  METALLURGY 

has  been  found  in  most  all  of  the  Western  states,  and  it  has 
been  imported  from  South  America  and  the  East. 

The  properties  of  tungsten  do  not  permit  of  any  economic 
use  of  the  metal  except  in  alloys.  It  has  a  bright-gray  color 
and  high  luster,  and  is  hard  and  brittle.  It  is  unaltered  in  the 
air,  except  at  high  temperatures,  when  it  is  converted  into  the 
trioxide.  The  melting  point  of  tungsten  is  about  1,700°  C. 

Tungsten,  finding  its  chief  application  in  the  manufacture  of 
tool  steel,  is  generally  prepared  as  an  alloy  with  iron.  The  ore 
is  mixed  with  carbon  and  smelted  in  an  electric  furnace. 

Molybdenum  occurs  chiefly  as  the  sulphide  in  the  mineral 
Molybdenite  (MoS2).  It  is  also  found  as  the  oxide  in  smaller 
quantities.  Molybdenum  ores  are  found  in  Arizona,  California, 
and  other  Western  states.  The  ore  is  also  imported. 

In  its  properties  molybdenum  resembles  tungsten,  being  of 
a  light-gray  color,  hard  and  brittle.  The  melting  point  which 
is  very  high,  has  not  been  accurately  determined.  Molybdenum 
is  used  like  tungsten,  in  the  manufacture  of  special  steels.  It  is 
prepared  by  similar  methods. 

Vanadium  occurs  as  the  oxide,  associated  with  iron,  lead,  zinc, 
copper  and  other  metals.  Deposits  of  vanadium  have  been 
found  in  Arizona,  Mexico,  Argentine  Republic  and  elsewhere. 

The  color  of  vanadium  is  light-gray,  and  it  is  slightly  crys- 
talline. It  is  hard  and  unworkable,  and  melts  at  about  1,700°  C. 
It  oxidizes  spontaneously  in  the  air  and  rapidly  at  high  tempera- 
tures. At  a  red  heat  it  combines  with  nitrogen. 

Vanadium  is  usually  prepared  as  an  alloy  with  iron.  This 
is  done  by  reducing  the  oxide  in  an  electric  furnace  with  car- 
bon. Molten  iron  is  added  to  prevent  oxidation  of  the  vanadium. 
It  may  also  be  reduced  in  a  crucible  with  aluminum,  the  principle 
being  the  same  as  that  used  in  Goldschmidt's  experiment.  (See 
p.  290). 

Platinum. — The  only  ore  of  platinum  is  native.  It  is  usually 
alloyed  with  the  other  metals  of  the  platinum  group.  Among 
these  the  best  known  are  iridium,  rhodium,  palladium  and 
osmium.  Platinum  is  usually  recovered  from  alluvium,  ir? 
which  a  natural  concentration  has  taken  place.  It  has  been 


NICKEL,    ALUMINUM,    MANGANESE,    ETC.  28 1 

found  in  the  gold-bearing  sands  of  California,  Canada,  Mexico 
and  elsewhere.  By  far  the  most  important  deposits  of  platinum 
yet  discovered  are  in  the  Ural  Mountains. 

The  chief  properties  to  which  platinum  owes  its  applications 
are  its  high  fusion  point,  malleability  and  its  inertness  toward 
chemical  agents  in  general.  It  has  about  the  hardness  of  cop- 
per and  can  be  worked  cold.  The  melting  point  is  about 
I'775°  C.  Platinum  is  not  oxidized  at  any  temperature  nor  is 
it  acted  on  by  any  single  acid.  It  is  attacked  and  dissolved  by 
aqueous  solutions  containing  chlorine. 

In  the  extraction  of  platinum  the  ores  are  concentrated  by 
washing,  and  then  smelted  or  treated  by  a  leaching  process. 
If  the  former  method  is  used  the  ore  is  smelted  in  crucibles  with 
lead  or  lead-bearing  material,  and  the  work-lead  obtained  is 
cupelled.  With  sufficiently  high  temperatures,  as  are  attainable 
in  electric  furnaces  and  with  the  oxy-hydrogen  flame,  platinum 
may  be  removed  from  the  ore  gangue  by  simple  fusion.  The 
usual  method  for  extracting  it  is  to  treat  the  ore  with  aqua 
legia,  which  converts  the  metal  into  a  soluble  chloride.  After 
prolonged  digestion  the  liquid  is  separated  from  the  gangue  and 
ammonium-platinic  chloride  is  precipitated  by  adding  ammonium 
chloride.  The  precipitate  is  dried  and  the  platinum  is  recovered 
from  it  in  an  electric  or  oxy-hydrogen  furnace. 


CHAPTER  XXVIII 


ALLOYS 

The  manufacture  of  alloys  is  a  very  ancient  art  and  one 
which  has  been  known  even  to  savage  people.  No  doubt  many 
of  the  ancient  alloys,  of  which  preserved  specimens  bear  record, 
'were  supposed  to  contain  but  one  metal,  or  else  no  method  was 
known  by  which  the  components  could  be  separated.  The  ex- 
istence of  some  alloys  might  be  accounted  for  by  the  smelting 
of  mixed  ores  or  ores  containing  more  than  one  metal.  Brass 
was  made  long  before  zinc  was  recognized  as  a  separate  metal. 
The  bronzes  and  alloys  of  the1  precious  metals  are  well  known 
examples  of  early  manufacture.  While  the  manufacture  of 
alloys  for  ornamental  purposes  was  borrowed  from  the  ancients, 
the  development  of  the  more  useful  properties  in  metals  by  al- 
loying is  peculiarly  a  modern  practice. 

Properties. — The  great  alterations  in  the  properties  of  metals 
when  alloyed  has  been  previously  shown.  It  has  also  been 
shown  that  many  of  the  most  useful  properties  may  be  devel- 
oped in  this  way.  Some  idea  of  the  possibilities  along  this  line 
may  be  formed  by  considering  the  great  number  of  mixtures 
of  the  common  metals  that  are  possible  if  the  ratios  be  varied. 
The  properties  of  an  alloy  can  not  be  anticipated  from  a  con- 
sideration of  the  properties  of  its  constituents.  In  binary  al- 
loys some  of  the  properties  may  be  intermediate  between  those 
of  the  two  metals,  while  the  other  properties  differ  entirely 
from  those  of  either.  The  color  is  in  some  instances  what 
would  be  expected  from  the  colors  of  the  separate  metals,  but 
there  are  numerous  instances  in  which  the  color  bears  no  re- 
lation at  all  to  that  of  either  constituent.  The  tenacity,  elastic- 
ity, ductility  and  hardness  may  fall  between  or  be  either  greater 
or  less  than  those  properties  in  the  single  metals.  The  fusion 
point  is  usually  lower  than  the  mean  of  the  two  and  often  be- 
low'that  of  the  more  fusible  metal.  Electric  conductivity  is 
generally  diminished  by  alloying,  sometimes  to  a  remarkable 


ALLOYS  283 

degree.  The  specific  gravity  of  an  alloy  is  usually  lower  than 
the  mean  of  its  constituents. 

Some  metals  are  rendered  more  active  toward  chemical 
agents  by  alloying.  On  the  other  hand,  it  is  possible  in  many 
cases  to  protect  metals  against  chemical  action  by  alloying  them 
with  metals  which  resist  corrosion. 

Constitution  of  Alloys. — It  has  been  shown  that  some  metals 
unite  with  greater  energy  than  others  do,  resembling  chemical 
affinity,  and  that  some  do  not  appear  to  alloy  with  each  other  at 
all.  Further,  it  has  been  shown  that,  although  molten  metals  may 
be  mixed  in  all  proportions,  it  does  not  follow  that  the  mixture 
will  remain  homogeneous.  The  well  known  processes  of  liqua- 
tion depend  upon  the  fact  that  the  liquid  metals,  from  lack  of 
affinity  for  each  other,  separate  by  gravity  in  rather  distinct 
layers.  Upon  solidifying  a  still  further  separation  may  take 
place,  just  as  chemical  salts  of  different  melting  points  or 
solubilities  may  be  separated,  by  crystallization.  In  aqueous 
solutions  the  medium  from  which  any  substance  is  crystallized 
is  called  the  mother  liquor.  Metals  when  fused  together  partial- 
ly or  entirely  dissolve  each  other,  and  the  medium  from  which 
metals  crystallize  is  called  the  mother  metal.  The  greater  the 
difference  between  the  melting  points  of  the  metal  which 
separates  and  the  mother  metal  the  more  complete  will  the  sepa- 
ration be. 

Alloys  are  regarded  by  some  authorities  as  being  analogous  to 
aqueous  solutions  of  salts,  and  to  strengthen  this  theory  at- 
tempts have  been  made  to  decompose  molten  alloys  by  electrol- 
ysis, but  so  far  without  success.1  Matthiessen's  view,  which 
is  generally  accepted,  is  that  metals  pass  into  an  allotropic  form 
when  they  alloy.  Evidence  of  this  is  furnished  by  experi- 
ments in  which  certain  metals  are  released  from  alloys  or 
amalgams  by  means  which  could  not  in  themselves  alter  the 
metals,  and  they  are  found  to  have  assumed  an  allotropic  form. 
There  are  but  few  instances  in  which  metals  form  true  com- 
pounds with  each  other.  They  do,  however,  alloy  in  definite 
proportions,  the  alloys  possessing  definite  properties.  A  jnix- 
1  See  Roberts- Austen's  Metallurgy,  p.  104. 


284  METALLURGY 

ture  of  two  metals  in  definite  ratio  and  melting  at  a  constant 
temperature  is  termed  an  eutectic  alloy.  The  eutectic  may  be 
either  a  conglomerate  of  the  metals  or  a  solid  solution.  In  the 
former  the  distinct  metals  may  be  seen  with  the  aid  of  a  micro- 
scope, but  this  is  not  possible  in  the  latter.  Solid  solutions  are 
not  necessarily  utectiferous,  but  they  may  contain  metals  in 
varying  ratios,  depending  upon  solubilities.  If  crystallization 
of  a  solid  solution  takes  place  the  form  will  approach  that  of 
the  metal  which  predominates.  While  it  is  true  that  metals 
often  unite  in  definite  ratios,  these  bear  no  relation  to  the 
atomic  weights,  and  there  is  no  convincing  evidence  of  chemical 
action. 

Cooling  Curves. — A  great  deal  has  been  learned  about  metals 
and  their  alloys  by  noting  their  behavior  while  cooling,  especial- 
ly in  the  rate  of  cooling.  The  rate  of  cooling,  as  determined  in 
any  experiment,  is  conveniently  plotted  on  cross-ruled  paper 
by  using  the  vertical  distances  to  denote  measurements  of 
temperature  and  the  horizontal  distances  to  denote  measure- 
ments of  time.  The  temperature  of  the  cooling  mass  is  read 
from  a  pyrometer  at  certain  intervals  and  marked  at  the  proper 
points  on  the  paper.  At  the  end  of  the  experiment  the  points 
are  connected  by  a  line  whose  direction  shows  graphically  the 
changes  of  temperature  in  the  given  time. 

When  a  substance  which  does  not  undergo  physical  or 
chemical  change  is  cooled  from  a  state  of  fusion  to  the  freezing 
point,  the  line  of  cooling  is  plotted  as  a  continuous  curve.  Thus, 
in  cooling  molten  tin  from  a  temperature  of  264  to  224,  the  line 
AB  is  described  (Fig.  86).  The  point  B  is  below  the  tempera- 
ture at  which  tin  freezes,  which  is  231.  When  freezing  com- 
mences it  proceeds  rapidly,  and  the  heat  evolved  raises  the 
temperature  of  th,e  metal  to  the  freezing  point.1  The  phenom- 
enon of  a  liquid  cooling  below  its  normal  freezing  point  and 
remaining  liquid  is  known  as  sur fusion.  After  surfusion  the 
freezing  may  be  started  by  adding  some  of  the  substance  in  the 

1  It  should  be  understood  that  freezing  is  a  change  by  which  heat  is 
evolved. 


ATXOYS 


solid  form  or  by  agitation.1  The  line  CD  marks  the  freezing 
of  the  tin.  The  line  shows  but  slight  fall  in  temperature,  since 
the  cooling  is  arrested  by  the  heat  evolved  in  the  change  from 
liquid  to  solid.  The  greater  the  mass  of  the  liquid  the  longer 
will  this  line  be.  The  cooling  of  the  solid  tin  is  represented  by 
the  regular  curve  DE. 

Fig.  87  represents  the  cooling  of  an  alloy  of  tin  and  copper. 
Here  the  line  AB,  instead  of  being  a  continuous  curve,  is  re- 

c° 

270 

A 

250 
240 


230 
220 
210 


200 


190 


\ 


\ 


\ 


\ 


/  2  3 

Min  ute  S 

Fig.  86. 
Tin  Cooling  Curve.     (Alloys  Research  Committee). 

versed  at  B.  This  change  is  accounted  for  in  the  freezing  out 
of  pure  tin.  The  phenomenon  of  surfusion  occurs  as  before, 
and  this  is  followed  by  the  freezing  of  the  tin-copper  alloy. 

Conditions  under  which  Metals  Unite  to  Form  Alloys. — i. 
Metals  may  be  made  to  unite  when  one  or  both  are  in  the  molten 
state.  The  method  of  making  alloys  by  fusion  is  most  familiar. 
1  Glacial  acetic  acid  freezes  at  17°.  It  may,  however,  be  cooled  consid- 
erably below  that  temperature  without  solidification.  If  under  these  con- 
ditions a  frozen  crystal  is  introduced  or  the  liquid  is  agitated,  the  whole 
freezes  almost  instantaneously. 


286 


METALLURGY 


Union  takes  place  when  both  or  all  constituents  are  in  the 
liquid  state,  or  when  one  is  liquid  and  the  others  solid  as  in  the 
formation  of  amalgams  or  any  alloys  at  a  temperature  below 
the  melting  point  of  one  of  the  metals. 

2.  The  union  of  metals  may  be  brought  about  at  ordinary 
temperatures  by  compression.  This  appears  to  be  due  directly 
to  the  property  of  flow  in  metals.  Lead  and  tin  sheets  may  be 
united  under  comparatively  slight  pressure,  while  such  brittle 
metals  as  antimony  and  bismuth  may  be  alloyed  by  subjecting 


Fig.  87. 
Tin-Copper  Alloy  Cooling  Curve.     (Alloys  Research  Committee). 

.them  to  powerful  pressure.  A  solid  block  of  bismuth  has  been 
obtained  under  a  pressure  pf  6,000  atmospheres  from  the  crys- 
talline powder. 

3.  Alloys  may  be  made  electrochemically  by  the  simultaneous 
deposition  of  the  metals  from  the  solutions  of  their  salts.  Al- 
loys made  in  this  way  appear  not  to  differ  from  those  of  the 
same  composition  prepared  by  fusion. 

THE  PREPARATION  OF  ALLOYS  ON  THE  INDUSTRIAL  SCALE 

In  the  classified  list,  given  below,  will  be  found  the  analyses 
of  some  of  the  more  important  alloys.  The  composition  of 


ALLOYS 


287 


Chromium 

3.00 

Chromium 

1.  00 

(Nickel               2.00) 

Chromium 

3-70 

(Tungsten        10.80) 

Chromium 

3.00 

(Molybdenum  4.25) 

Manganese 

12.00 

Nickel 

3-50 

Vanadium 

1.  00 

Copper  Zinc 

Tin 

yo.O 

30.0 

65.0 

35-0 

91.0 

9.0 

J6S 

23-5 

82.0 

2.O 

16.0 

77.0 

8.0 

50.0 

31-9 

3-1 

50.0 

25.0 

75-o 

95-o 

2-5 

2-5 

79-7 

10.0 

90.0 

88.0 

IO.O 

Lead 


many  of  the  alloys  of  the  same  name  is  quite  variable,  this 
being  especially  true  of  the  bearing  metals.  The  analyses  given 
are.  but  typical  in  some  instances.  New  alloys  are  being  in- 
troduced every  year,  and  it  would  be  impracticable  here  to  list 
all  that  are  now  in  use. 

IRON  SERIES.— (SPECIAL  STEELS). 

Alloying  Metal.     Per  Cent.  Remarks. 

Aluminum  0.15  See  Jour.  Iron  and  Steel  Inst., 

1890,  2,  161. 
Copper  4.00  Jour.    Iron    and    Steel    Inst., 

1907,  2,  i. 

Tool  steel. 

Armor  plate  and  projectile. 
Tool  steel. 
«         « 

(Hadfield). 

Ordnance,  nickel  steel. 
Jour.    Iron    and    Steel    Inst., 
1905,  2,  118. 
COPPER  SERIES. 

Nickel  Remarks 

Typical  brass 

Mosaic  gold. 

Gun  metal  (Bronze) 

Bell 

Bearing  metal  for  heavy  bearings 
15-0  "  "     (P.  R.  R.  "B") 

14.8  German  silver 

25.0  Bearing  metal 

25.0  U.  S.  coin 

«        « 

9.5  (Phosphorus    0.8)  Phosphor-bronze 
(Aluminum    10.0)  Aluminum  bronze 
(Manganese     2.0)  Manganese     " 
TIN-LEAD  SERIES. 

Remarks 
Soft  Solder 

Babbitt  Metal,1  for  bearings 
Britannia  Metal,  for  bearings 
White 

Antifriction  "         "         " 
Magnolia       "         "         " 
Type 
Pewter 
Shot 

1  The  original  composition  of  this  alloy  is  not  known.     Ledebur  gives- 
Zinc,  69.0;  Tin,  19.0;  Copper,  4.0;  Antimony,  3.0. 


Tin 

Lead 

Antimony 

50.0 

50.0 

45-5 

40.0 

13.0 

(Copper 

1-5  ) 

90.0 

IO.O 

82.0 

12.  0 

(Copper 

6.0  ) 

40.0 

55-o 

5-o 

4-75 

80.0 

15-0 

(Bismuth 

0.25) 

3-o 

82.0 

15-0 

80.0 

20.  o 

99-7 

(Arsenic 

0-3  ) 

288 

BISMUTH  SERIES. 

Bismuth  Lead  Tin  Cadmium  Remarks 

50.0  31.25  18.75  Melts  at  95°  C  (Newton) 

50.0  28.10  24.64  "     "  100°       (Rose) 

50.0  25.0  25.0  "     "    93°       (Darcet) 

50.0  27.0  13.0          10.0          "     "     60°       (Lipowitz) 

PRECIOUS  METALS. 

Gold              Silver  Copper  Remarks 

90.0  10.0  U.  S.  coin 

90.0  10.0                  "         " 

50.0  50.0  i2-carat 

66.7  33.3  i6-carat 

75.0  25.0  i8-carat 

NOTES  ON  THE  MANUFACTURE  OF  ALLOYS 

Alloys  are  prepared  commercially  by  the  fusion  method, 
which  is  simplest  and  most  effective.  The  two  or  more  metals 
may  be  melted  together  or  melted  separately  and  then  mixed. 
A  flux  or  covering  is  used  with  oxidizable  metals,  and  in  some 
instances  measures  must  be  taken  to  prevent  volatilization  and 
the  absorption  of  gases.  Processes  in  which  one  or  more  of 
the  metals  are  smelted  and  simultaneously  alloyed  are  common. 
On  account  of  the  difficulty  with  which  some  metals  are  made 
to  unite  and  the  tendency  toward  segregation,  it  is  impossible 
to  make  some  alloys  homogeneous  throughout.  The  rapid 
growth  of  manufactures  and  the  high  duty  now  required  of 
metals  are  directly  responsible  for  the  large  number  of  alloys 
which  the  market  affords,  as  well  as  for  their  quality. 

Alloy  Steels. — These  are  generally  prepared  by  adding  the 
alloying  metal  to  the  charge  of  steel  in  the  open  hearth  furnace, 
converter  or  crucible.  With  so  large  a  quantity  of  steel  as  is 
treated  in  the  open  hearth  or  converter,  the  metal  may  be 
thrown  into  the  ladle  as  the  steel  is  tapped.  This  method  has 
the  advantage  that  less  of  the  alloying  metal  is  oxidized,  though 
il  may  be  necessary,  for  the  sake  of  producing  a  uniform  alloy, 
to  mix  the  metals  in  the  furnace. 

Another  method  of  making  alloy  steel  is  to  reduce  the  alloy- 
ing metal  from  its  ore  in  contact  with  the  steel.  One  of  the 
processes  for  making  nickel  steel  is  to  charge  nickel  ore  into 


AIXOYS  289 

the  open  hearth,  the  nickel  toeing  reduced  by  the  carbon  present 
at  the  beginning  of  the  heat. 

Brass. — In  the  melting  and  casting  of  brass  the  appliances 
used  are  similar  to  those  used  in  iron  founding,  except  that  in 
brass  founding  the  appliances  are  generally  smaller  and  less  ela- 
borate. Brass  is  melted  in  crucibles,  cupolas  and  other  styles  of 
furnaces,  crucibles  being  the  most  common.  The  copper  is  first 
melted  or  heated  to  near  the  melting  point,  and  then  the  zinc  is 
added.  If  the  brass  is  to  contain  a  large  excess  of  copper  the 
zinc  may  be  added  cold,  otherwise  it  should  be  fused  before  the 
mixing.  On  account  of  its  volatility  a  larger  amount  of  zinc 
is  charged  than  is  required  in  the  brass. 

Oxidation  of  the  metals  in  brass  founding  is  largely  prevented 
by  the  use  of  fluxes  such  as  glass,  chloride  of  ammonia  and 
fluorspar.  The  oxides  may  be  removed  from  the  fused  alloy  by 
adding  a  small  amount  of  aluminum  or  magnesium. 

Other  Alloys. — In  making  bronze  the  tin  is  melted  in  a 
separate  vessel  and  added  to  the  molten  copper.  The  mixture 
must  be  well  stirred  to  make  it  homogeneous.  Somewhat  the 
same  procedure  is  followed  in  alloying  copper  and  lead.  Bab- 
bitt metal,  containing  copper,  antimony  and  tin,  is  prepared  by 
adding  the  antimony  to  the  copper,  which  is  already  fused,  and 
then  adding  the  tin  in  two  portions.  After  the  first  portion  is 
added  the  mixture  is  stirred  for  some  time  while  the  tempera- 
ture is  maintained  at  dull-redness.  The  addition  of  the  second 
portion  is  also  followed  by  stirring  to  prevent  the  metals  from 
separating. 

Phosphorus  is  usually  introduced  into  alloys  in  the  form  of 
a  phosphide.  Phosphides,  such  as  phosphor-copper  and  phos- 
phor-tin are  prepared  by  adding  stick  phosphorus  to  the  metal. 
The  metal  being  fused  in  a  crucible,  the  phosphorus  is  im- 
mersed in  the  bath  by  means  of  an  inverted  iron  cup,  and  held 
there  until  it  is  absorbed. 

WELDING 

The  weldable  metals  are  those  which  can  be  brought  into 
molecular  union  under  pressure.  For  practical  purposes  it  is 
necessary,  in  most  instances,  to  heat  the  pieces  to  be  welded  to 

10 


290  METALLURGY 

the  forging  temperature,  when  they  will  unite  under  slight 
pressure.  In  ordinary  welding  operations  the  pieces  to  be 
united  are  heated  in  a  furnace  to  the  proper  temperature,  and 
forced  together  between  rolls  or  by  hammering.  It  is  neces- 
sary that  the  surfaces  at  the  point  of  contact  be  free  from  scale 
or  other  solid  matter.  Sometimes  fluxes,  such  as  borax  and 
ammonium  chloride  are  used  to  dissolve  the  metallic  oxide, 
and  the  slag  that  forms  is  squeezed  out  in  the  operation  of 
welding.  The  surfaces  are  prepared  beforehand  so  that  they 
will  fit  together,  both  being  forged  flat  or  into  corresponding 
shapes.  The  pieces  are  either  lapped  or  united  at  the  ends, 
giving  rise  to  the  terms  "lap"  and  ubutt"  welding. 

Electric  Welding. — This  method  of  welding  makes  use  of  the 
heat  from  an  electric  arc.  The  pieces  to  be  joined  are  gripped 
by  bronze  clamps,  which  are  connected  with  the  terminals  of 
a  dynamo.  One  of  the  clamps  is  arranged  to  move  with  the 
piece,  so  that  any  space  needed  can  be  opened  between  the  sur- 
faces to  be  joined,  or  the  pieces  brought  together  under  power- 
ful pressure.  The  surfaces  having  been  properly  prepared,  are 
held  in  contact,  and  the  current  is  turned  on.  The  movable 
piece  is  then  drawn  back  to  form  the  arc.  The  heat  developed 
soon  brings  the  surfaces  to  the  required  temperature,  when 
they  are  pressed  together  to  make  the  weld. 

Thermit  Welding. — This  process  is  the  invention  of  Gold- 
schmidt.  It  employs  a  mixture  of  iron  oxide  with  pulverized 
aluminum,  to  which  the  inventor  gave  the  name  "Thermit."  In 
the  welding  operation  the  thermit  is  supported  above  the  work 
in  a  funnel-shaped  crucible,  and  a  sand  mold  is  fitted  about  the 
pieces  to  be  joined  so  that  the  liquid  iron  which  fills  it  will  come 
in  contact  with  enough  area  of  both  pieces  to  make  a  strong 
union.  The  thermit  is  kindled  with  a  mixture  of  aluminum-barium 
peroxide  and  the  aluminum  continues  to  burn  with  great  inten- 
sity to  aJlumina,  and  reduces  the  iron.  A  small  amount  of  metal- 
lic iron  is  sometimes  added  to  the  thermit  to  prevent  the  tem- 
perature from  running  too  high.  The  iron  is  tapped  into  the 
mold,  and  coheres  to  the  pieces  which  themselves  become  soft- 
ened on  the  surface  by  the  heat.  The  thermit  process  is  used 


ALLOYS  291 

for  welding  rails  and  large  forgings  and  castings  that  have  been 
fractured.  The  latter  application  is  especially  useful  in  cases 
where  other  methods  of  welding  would  require  the  dismantling 
of  cumbersome  machinery. 

PLATING 

Base  metals  and  those  which  are  corrodible  are  covered  with 
a  more  expensive  metal  for  the  purpose  of  ornament  or  for 
protection  against  rust.  The  thin  sheet  of  metal  does  not 
adhere  to  the  other  metal  as  paints  do,  but  it  forms  a  surface 
alloy  or  molecular  union,  which  cements  the  two  metals  to- 
gether. Such  plating  will  not  scale  off.  The  metals  copper, 
nickel,  silver  and  gold  are  chiefly  employed  for  ornamental 
work,  and  for  protection  against  rust,  zinc  and  tin  are  most 
cr.mmonly  used.  Lead,  copper  and  nickel  are  also  used  for 
piotective  plating. 

The  necessaiy  conditions  in  any  plating  process  are  that  the 
surface  of  the  metal  to  be  plated  be  clean,  and  that  the  metal 
to  be  deposited  be  pure  and  in  the  proper  physical  condition 
for  forming  an  alloy  with  the  other  metal.  These  conditions 
are  brought  about  in  two  ways  on  the  industrial  scale.  THie 
metal  to  be  plated  is  either  dipped  in  a  molten  bath  of  the  other 
metal  or  placed  as  a  cathode  in  a  solution,  from  which  the 
other  metal  is  deposited  by  the  aid  of  an  electric  current.  These 
are  known  as  dipping  and  electrolytic  processes. 

Tin  Plating. — The  most  important  industry  of  this  class  is 
the  plating  of  sheet  iron  for  the  manufacture  of  roofing  and 
tin  ware.  Th,e  sheet  iron  or  steel,  having  been  rendered  hard  by 
cold  rolling,  is  toughened  by  annealing.  The  annealing  is 
done  in  a  closed  chamber  to  check  oxidation.  The  sheets  are 
then  immersed  in  dilute  sulphuric  or  hydrochloric  acid  to  re- 
move the  scale.  This  is  termed  "pickling."  The  last  trace 
of  acid  is  washed  from  the  sheets  after  immersing  them  in  lime 
water  and  rinsing,  and  they  are  now  ready  for  plating. 

The  tin  is  melted  in  a  deep  pot,  a  section  of  which  is  shown 
in  Fig.  88.  In  the  opening  by  which  the  sheet  is  introduced 
the  tin  is  covered  with  a  flux  of  zinc  chloride  and  a  small 
amount  of  ammonium  chloride.  The  direction  which  the  sheet 


292 


METALLURGY 


takes  is  indicated  by  the  lines  with  the  arrow  heads.  The 
sheet  is  turned  and  lifted  by  aid  of  the  tool  until  it  is  gripped 
by  the  first  pair  of  rolls.  Four  pairs  of  rolls  are  arranged  as 
shown  in  the  upper  part  of  the  pot.  These  rolls  revolving1  in 
the  directions  indicated,  carry  the  sheet  out  of  the  bath,  and 
give  an  even  coat  of  tin.  The  rolls  are  surrounded  by  molten 
grease. 


Fig.  88 
Tinning  Pot.     (Harbord  and  Hall). 

The  flux  of  zinc  and  ammonium  chlorides,  through  which  the 
sheet  passes  as  it  is  introduced  into  the  tinning  pot,  serves  to 
cleanse  the  surface  of  the  iron  and  to  remove  oxides  from  the 
bath.  The  grease,  through  which  the  sheet  passes  as  it  leaves 
the  bath,  does  not  mix  with  the  tin,  but  prevents  exposure  while 
the  excess  of  tin  is  being  removed  by  the  rolls.  The  sheets  are 
cleaned  by  passing  them  through  wheat  bran  and  then  brush- 
ing. This  is  done  entirely  by  machinery  in  modern  plants. 

Zinc  Plating. — Though  of   comparatively  recent  origin,   zinc 


ALLOYS  293 

plate  has  now  the  most  extensive  usage.  This  is  due  to  the  rel- 
atively low  cost  of  zinc  and  to  the  economy  in  the  manufacture 
of  zinc  plate.  The  process  of  plating  with  zinc  is  commonly 
called  "galvanizing/7  from  the  fact  that  iron  and  zinc  together 
form  a  galvanic  couple.  Zinc  is  the  opposite  of  tin  in  its  being 
electropositive  to  iron.  For  this  reason  it  is  attacked  first  when 
the  two  metals  are  exposed  to  corrosive  agents,  and  the  iron 
is  preserved.  Zinc  plate  has  now  largely  superceded  tin  plate 
for  outside  work,  but  it  can  not  be  used  for  cans  in  which  food 
is  stored,  since  meat  and  vegetable  acids  attack  zinc  and  the 
salts  formed  are  poisonous.  Zinc  plaice  is  manufactured  both 
by  the  dipping  and  the  electrolytic  processes. 

The  Dipping  Process. — The  iron  or  steel  sheets  are  prepared 
as  for  tin  plating.  The  zinc  is  melted  in  a  vessel  constructed 
of  soft  iron  plates.  It  is  covered  with  a  flux  of  ammonium 
chloride,  which  serves  as  a  protective  coating  and  to  dissolve 
oxides.  The  sheets  are  introduced  into  the  bath  and  carried 
through  by  means  of  guide  rolls,  the  speed  of  which  determines 
the  length  of  time  that  the  iron  is  kept  in  contact  with  the  zinc. 
The  thicker  the  sheets  the  longer  time  will  be  required,  since 
it  is  necessary  for  the  iron  to  attain  the  temperature  of  the  zinc 
before  the  latter  will  adhere  perfectly. 

The  Electrolytic  Process. — This  process,  which  is  otherwise 
known  as  "cold  galvanizing,"  is  now  carried  on  so  successfully 
as  to  compete  with  the  dipping  process.  Points  in  favor  of 
cold  galvanizing  are  that  the  toughness  of  the  iron  is  not  im- 
paired as  is  done  by  dipping  it  in  the  hot  zinc,  and  that  the 
plate  generally  adheres  better.  The  electrolytic  process  is, 
however,  slower  and  more  costly  than  dipping,  and  it  is  not  so 
suitable  for  plating  articles  of  irregular  shapes,  since  as  cathodes 
they  cause  unequal  resistance  of  the  current  in  the  electrolyte 
and  consequently  an  uneven  deposition  of  the  zinc. 

The  electrolyte  used  in  galvanizing  is  a  solution  of  zinc  sul- 
phate or  chloride  containing  an  excess  of  the  acid.  The  anodes 
are  cast  from  spelter.  In  early  practice  much  difficulty  was 
met  with  in  obtaining  an  even  and  adherent  coating  on  account 
of  the  electrolyte  becoming  impoverished  in  zinc.  A  uniform 


294  METALLURGY 

composition  with  the  required  amount  of  zinc  could  not  be 
maintained  by  any  arrangement  of  the  anodes.  The  difficulty 
was  overcome  by  Cowper  Coles,  whose  process  consists  in 
pumping  the  electrolyte  through  tanks  containing  zinc  dust. 
A  large  amount  of  zinc  is  thus  added  to  the  solution  and  its 
composition  is  kept  uniform  by  the  circulation. 

Plating  with  Other  Metals. — In  plating  with  nickel,  copper, 
silv(er  and,  gold,  electrolytic  methods  are  now  more  commonly 
used  than  those  of  dipping.  Nickel  is  used  chiefly  for  plating 
iron,  copper  and  brass.  It  is  deposited  from  an  ammoniacal 
solution  of  the  sulphate.  A  better  plate  of  nickel  on  iron  is 
obtained  by  first  plating  the  iron  with  copper  and  then  plating 
with  the  nickel.  Copper  is  deposited  from  an  acid  solution  of 
the  sulphate.  Silver  and  gold  are  commonly  deposited  from 
cyanide  solutions.  Brass,  german  silver  and  some  other  alloys 
may  be  deposited  electrochemically  if  it  is  desirable  to  use  them 
for  plating. 


INDEX 


A 

ACID,  Bessemer  process 137-143 

open  hearth  process 145-150 

refractory  materials 10-13 

Air  pyrometer 20 

"    reduction  process 215 

Alloying  property  of  metals 7 

Alloys 282-294 

"      constitution  of       283 

"      preparation  of 286 

properties  of 282 

steel 287, 288 

"      tables  showing  composition 287-288 

Alumina  as  a  refractory  material 12,  14 

"        in  iron  blast  furnace  process 82 

Aluminum,  effect  on  iron 75 

extraction  of 276-278 

history  of 275 

"           ores 276 

properties  of 276 

steel - 287 

use  in  casting  steel 149 

Amalgamating  barrel 253 

pan 250 

Amalgamation 47 

of  gold  ores 260-264 

of  silver  ores 246-255 

American  bloomary 121 

"         hearth 216 

"         rail  specifications 169 

Ampere 204 

Annealing  clay  retorts 236 

"          iron  castings 118 

steel 166 

Anode 204 

"      mud 207, 208 

Anthracite      28 

Antimony,  effect  on  copper 172 

"          effect  on  lead 210 

"          in  copper  smelting  process 198 

"          in  copper  refining  procesg 207 

"           in  lead  smelting 221 

"          removal  from  lead 224 

Appolt  coke  oven , 35 

Argentite 245 

Arrastra 248 

Arsenic,  effect  on  copper 172 

"       effect  on  lead 210 

"       in  copper  smelting  process 198 

"       in  copper  refining  process 207 


296  INDEX 

Arsenic,  in  iron  blast  furnace  process 

"        in  lead  smelting 22r 

Atwater,  on  by-product  coke 39 

Augustin  process • 

O 

BAG  filters  for  lead  fume 

Barrel  amalgamation 

Bar  screens 

Basic  Bessemer  process 

"     open  hearth  process 150-154 

"     refractory  materials I3~I4 

Bauxite H,  276 

Beehive  coke  oven 

Belgian  process    ....          _ 

Bell  charging  apparatus  for  iron  blast  furnaces 77*  91 

Bell,  Sir  I,.,  fuel  calculations 109 

Bertrand-Thiel  process *57 

Bessemer  converters ....  138,  193 

"         process,  copper !93 

process,  steel i37~M4 

"         Sir  H.,  process  for  making  steel 13? 

Billets ifil 

Bisbee  converter 193 

Bismuth,  effect  on  copper 172 

"         effect  on  lead 210 

"        in  copper  refining  process 207 

Bituminous  coal 27 

Black  tin 241 

Blake  ore  crusher 5° 

"      W.  P.,  method  of  concentrating  sulfides 333 

Blastfurnaces (See  copper,  iron  and  lead)  61,77,  87.  II3,  1$%,  189,  191,  193.  217 

"     management  of  in  iron  smelting 101 

"     temperature  records  of 102 

Blende 231 

Blister  copper 188 

"      steel i33 

Blooms !6i 

Blooming  mill 161 

Blowholes 75i  IIQ,  Z58 

Blowing  engines 95-97 

"       in  iron  blast  furnaces 97 

Blue  metal 174 

"     powder : 238 

Bogie  for  steel  ingots 159 

Bosh  construction  in  iron  blast  furnaces 87 

"    plates 88-89 

Boss  process •. 253 

Brass 288,  289 

Breaking  ores 50 

Briquettes,  peat 25 

flue  dust 108 

Bristol  pyrometer 21 

Brittleness  in  metals 6 

Brown  hoist  and  distributor 91 

"      ore  roaster 178 

Bruckner  ore  roaster 178 


INDEX  297 

Burdening  iron  blast  furnaces *  ...  98-100 

By-product  coke  ovens 35-40 

C 

CAKING  coal '. 28 

Calamine     231 

Calcination 57 

Calcining  zinc  ores 233 

Calculation,  efficiency  of  gas  producers 42-44 

for  iron  blast  furnace  charge 98-100 

thermal  requirement  in  iron  blast  furnace  process 108-109 

Calorie 17 

Calorific  intensity 19 

Calorimetry 17-19 

Campbell  furnace 156 

Cannelcoal 27 

Carbon,  effect  on  iron 69-7*1  112,  166 

"        in  iron  blast  furnace  process 80 

"       in  open  hearth  process 152 

Carbon  in  steel 166 

Cast  iron , 110-120 

Catalan  forge 121 

Cathode 204 

Cementation  process 131-134 

Cement  carbon 71 

"      steel 133 

Cerusite *. 209 

Chalcocite 170 

Chalcopyrite '. 170 

Chamott 234 

Charcoal  in  iron  blast  furnace  process 101 

manufacture  of 25,  30-32 

Chemistry  of  Bessemer  steel  process 143,144 

"         of  copper  ore  roasting 182 

"         of  copper  smelting 188,  196 

"         of  iron  blast  furnace  process 79 

"         of  lead  smelting 188,  197-199 

"         of  open  hearth  process       151-154 

"         of  puddling  process 124 

"         of  silver  amalgamating  processes 254 

"         of  zinc  smelting 238 

-Chilian  mill 53 

Chills 117 

Chloridizing  copper  ores 200 

gold  ores 264 

silver  ores 247 

"            roasting 57.  200,  247 

Chrome  brick 15 

Chrome-iron  ore 14 

Chrome  steel 73-287 

Chromite     14, 67 

Chromium,  effect  on  iron 73 

in  iron  blast  furnace  process 83 

metallurgy  of 279 

Cinder » 15 

Cinnabar 242 

•Clay 11-13,  234 


298  INDEX 


Clay  iron  stone 67 

Coal 26-29 

"    in  iron  blast  furnace  process 101 

Coke  in  iron  blast  furnace  process 100 

"    manufacture  of 32-40 

"    quenching  machines 38 

Coking  coal .  28 

Cobalt 275 

"      removal  from  copper 207 

Cold  bending  test 5 

"    galvanizing 293 

Coles,  C.,  galvanizing  process 294 

Combined  carbon  in  iron 70 

Combustion  and  thermal  measurements 16-23. 

Compensator  for  Bristol  pyrometer 22 

Compression  of  liquid  steel 158 

tests     4 

Concentration  of  ores  (See  ore  dressing). 

Condenser  manufacture  (zinc) 235 

Conductivity  in  metals 8 

Converters  (Bessemer)     138-193 

Converter  dust 143 

slag 143 

Continuous  gas  producer 41 

"         heating  furnace 165 

"         open  heasth  process 165 

"         rolling  mill 164 

Cooling  curves 284 

Copee  coke  oven 35 

Copper  blast  furnaces 189-191 

"       extraction  of 184-200 

"        history  of ....'•• 170 

"       in  iron  blast  furnace  process 83 

ores 170 

"        properties  of 171-173 

"       refining  of 201-208 

"       removal  from  lead 224 

Cornish  process 216 

Cort's  puddling  process 122,125 

Cowles  Bros.'  process  for  smelting  aluminum 277 

Cowper  stove 93 

Cradle  for  washing  gold  ore 259 

Crucible  furnaces ^ 62,  135,  277 

"       process "  ......  134-136 

steel '.   .  i34 

Crucibles,  manufacture  of 134 

Cryolite 276 

Crystallization  of  metals i 

Cupellation 229 

Cupola,  copper 189 

iron II3 

Cuprite I7i 

Cyanide  process  for  treating  gold  ores 265-270 

process  for  treating  silver  ores 257 

ID 

DAM  used  in  casting  pig  iron io6> 


INDEX  299 

Damping  down  iron  blast  furnaces 98 

Density  in  metals 

Desilverizing  lead 225-230 

Destructive  distillation 3° 

Diagram,  showing  history  of  by-product  coke  oven  process 39 

"        history  of  open  hearth  heat 155 

Dipping  process  for  zinc  plating 293 

Direct  pouring  of  iron  in  Bessemer  process I38 

"     process  for  wrought  iron  and  steel 121,  124 

Distillation  furnaces 62,  228,  236,  243,  252 

Distribution  of  stock  in  iron  blast  furnaces 91 

Dolomite 14 

"       in  iron  blast  furnace  process 101 

Downcomer  dust 79>  IQ8 

Dredging 261 

Drop  testing 6,  120 

Dry  blast  apparatus 105 

"    puddling 125 

"    sand  molds "6 

Ductility  in  metals 5 

Duquesne  blast  furnace  hoist 9° 

Dust  catchers 91 

E 

ELASTICITY  in  metals 2 

Elastic  limit 2 

Electric  furnaces 63,  277 

"       resistance  pyrometer 21 

welding 290 

Electro-cyanide  processes 268-270 

Electrodes 204 

Electrolyte 204 

Electrolytic  preparation  of  alloys     286 

"           process  for  extracting  aluminum 276-278 

"           process  for  extracting  nickel 274 

process  for  plating  with  zinc 293 

"           refining  of  copper 203-208 

refining  of  gold  and  silver 271 

44           refining  of  lead 230 

Endothermic  reactions 16 

English  lead-smelting  furnace       214 

Equalizing  temperature  of  blast 103 

Eutectic  alloys 284 

Evaporative  power 19 

Exothermic  reactions 16 


FERRO-CHROME 73 

"        manganese  . 72>  2/9 

"        phosphorus 72 

"        silicon TI 

tungsten 74 

Fettling  for  puddling  furnace 127 

Fire-clay n 

Flouring  of  mercury 264 

Flow  in  metals 6 

Flue  dust    . 79.  108 


3OO  INDEX 

Fluorspar  .....................................  15,  151,  222 

Fluxes  ........................................  *5 

Flying  shears    ....................................  164 

Forehearths  .....................................  192 

Forges  ........................................  61,  121 

Forging  iron  and  steel  ................................  161-165 

Foundry  practice    ..................................  113-120 

Fracture  of  metals  ..................................  i 

"        tests  for  steel     ..............................  136-149 

Franklinite     ..............................   .,  ......  68,  231 

Free-milling  gold  ores     ................   .............  .   .  260 

Frue  vanner  ..............   .......................  55 

Fuels  ........................................    16,  24-45 

"     used  in  iron  blast  furnace  process     ......................  100 

Furnaces  .......................................  59-63 

Fusibility  of  metals  .................................  6 

Fusion  point  pyrometer  ...............................  20 

G 

GALENA    ......................................  209 

Galvanizing  .....................................  293 

Canister  .......................................  13,  139 

Garnierite  ........................  ..............  272 

Gas  as  a  fuel  .....................................  24 

"    producers            .................................  41,  45 

Gates  ore  crusher    .................................  50 

Gay  ley  bosh  plate  ..................................  89 

"       dry  blast  apparatus    .............................  105 

"       J.,  on  blowing  in  iron  blast  furnaces    ....................  97 

Gjers  kiln  ..............................  ........  60 

Goethite  .......................................  66 

Gold  dredge   .....................................  258 

extraction  of  ..................................  259-270 

"     in  copper  smelting  ..............................  199 

"     in  copper  refining  process  ...........................  202,  207 

"     ores    ......................................  258 

"     properties  of  ........................  ^  .........  258 

"     refining  of  ...................................  270 

Goldschmidt  process  .................................  290 

Grading  pig  iron  ...................................  in 

Graphitic  carbon,  effect  on  iron  ...........................  69 

Graphite  .......................................  14 

"       crucibles    ..................................  134 

Gray  iron  ................................  "  ......  70,  112 

Grizzly  ........................................  53 

Gyratory  crusher    ..................................  50 

ff 


73 

Hall  process  for  smelting  aluminum  ........................  277 

Hammer  forging  ..............................   .....  164 

Hand  picking  ores  ..................................  48 

reverberatory  furnace  .  ,   ...........................  176 

Hardening  carbon  in  iron  ..............................  71 

Hardness  in  metals    .................................  6 

Hartman,  J.  M.,  grading  iron  ............................  in 

Harreyizing  armor  plates  ..................  168 


INDEX  3OI 

Hausmanite 278 

Heap,  charcoal 31 

"      roasting 174 

Hearths 61 

lead 216 

Heat  conduction  p}'rometer 20 

"    regenerators 37,  63,  93-95,  145 

''    treatment  of  steel 165-168 

'    unit 17 

Hematite 65 

Herreshoff  furnace 180 

History,  Aluminum 275 

"        Bessemer  process ...       137 

"       copper 170,203 

"       iron 65,  121-122 

"        lead 209 

"       open  hearth  process 145 

"        zinc 231 

Hofmau,  H.  O.,  composition  of  lead  slags 222 

"         H.  O.,  roasted  lead  ore 213 

"         H.  O.,  lead  blast  furnace  charge    .  . 219 

Hoists  for  iron  blast  furnaces 90-91 

Horn  silver 245 

Horseshoe  roaster *.....  178 

Hot  blast,  management  of 95, 101 

"     blast  stoves 93 

Humidity  of  hot  blast  and  effect  of 104 

Huntington  mill 53,  264 

Hydraulicing 260 

Hydrogen,  effect  on  iron 75 

in  iron  blast  furnace  process 80 

I 

ILMENITE 67 

Impact  testing 119 

Ingalls,  W.  R.,  composition  of  clays 234 

Ingots 136, 159 

Inquartation •  .   .   .  271 

Iron  blast  furnace 77,  87 

"    blast  furnace  dust 79, 108 

"    blast  furnace  gas 85 

"    blast  furnace  plant 86 

"    blast  furnace  process 77-109 

"    blast  furnace  slag 83,  107 

"    extraction  of 77-109 

"    founding 113-120 

"    history  of 65, 121 

"    in  copper  refining  process 207 

"    mixer 138 

"    ores 65-68 

"    refining  of 124-169 

"    use  of  in  smelting  lead 221 

JAW  crusher 50 

Jig 54 

Jones  mixer 138 


3O2  INDEX 


KELLY,  Wm.,  process  for  refining  iron 137 

Kidney  ore 66 

Killing  steel  in  crucible  process 136 

Kilns 60 

Kish 69 

Krupp's  process  for  treating  armor  plates 168 

L 

LADLE  for  lead  matte 220 

"       for  pouring  steel 142 

Langley's  experiment  with  tungsten  steel 74 

Leaching  processes ^ 

"          processes  for  extracting  copper 199 

"          processes  for  extracting  gold 264-270 

"          processes  for  extracting  nickel 274 

"          processes  for  extracting  silver 255-257 

Lead  blast  furnace 217 

"    extraction  of 214-223 

"    fume 222 

"    history  of  .   .       209 

"    in  copper  smelting  process 198 

"    in  copper  refining  process 208 

"    ores  .   .   .   j> 209 

"    properties  of 209-211 

,     "    refining  of 224-230 

"    softening 224 

LeChatelier  pyrometer 21 

Lewis  and  Bartlett  process 222 

Lignite 25 

Lime  as  a  refractory  material 13 

"      in  iron  blast  furnace  process 82,  101 

"      in  lead  blast  furnace  process 221 

lyimonite 66 

Loam  molds 117 

Lodes 47 

Luce  and  Rozan  process 226 

yvi 

MAGNESIA  as  a  refractory  material 13 

in  iron  blast  furnace  process 82, 101 

"          in  lead  blast  furnace  process 221 

Magnetic  separation  of  ores 56 

Magnetism  in  metals 8 

Magnetite 66 

Malachite 171 

Malleability  in  metals 5 

Malleable  castings 118 

Manganese,  addition  to  steel 141 

effect  on  iron 72,  112,  149 

in  iron  blast  furnace  process 81 

in  open  hearth  process 153 

metallurgy  of 278 

steel 73,287 

Matte,  copper 174 

"      lead 220 

Matting  furnace 184 


INDEX  303 

McArthur-Forrest  process 265 

Mechanical  drawers  for  beehive  coke  ovens 35 

"           furnaces 62,  130,  138,  178,  180,  193 

puddling 130 

treatment  of  iron  and  steel 158-165 

treatment  of  metals 48 

Melaconite 171 

Mercury,  extraction  of 243-244 

"          recovery  from  amalgams 252 

"          refining 244 

Metal  expansion  pyrometer 20 

Micaceous  ore 66 

Mica  schist 13 

Mild  steel 131 

Milling  gold  ores 263 

Mineral  wool 108 

Mixer  for  pig  iron 138 

Mixing  iron 115-138 

Mixing  ores        57 

Modulus  of  elasticity 3 

Moisture  in  iron  blast  furnace 104 

Molds,  ingot 136-159 

"       used  in  iron  founding 116-118 

Molybdenum,  effect  on  iron 74 

"             metallurgyof 280 

steel 74 

Morgan  gas  producer 41 

Mortar,  stamp  mill 52 

Mottled  iron 112 

Muffle  furnaces 62, 125 

Muntz  metal 263 

Mushet  steel .   . 74 

N 

NATIVE  copper 170 

"       gold 258 

"       iron 65 

"       mercury 242 

"       silver 245 

Natural  gas 28 

Neutral  refractory  materials 14 

Nickel,  effect  on  iron 73 

extraction 273-275 

"        in  copper  smelting  process 198 

"       in  copper  refining  process 207 

"       ores 272 

steel 73,  287 

Nitrogen,  effect  on  iron 75 

"          in  iron  blast  furnace  process 80 

Nuggets 258 

O 

OCCIyUSION  in  metals 8,  75 

Optical  pyrometer 21 

Ore  dressing 46-58 

"    dressing,  copper  ores 173-183 

"    dressing,  gold  ores 259-261 


304  INDEX 

Ore  dressing,  iron  ores 68 

"    dressing,  lead  ores 211-213 

"    dressing,  silver  ores 247 

"    dressing,  zinc  ores    . 233 

Ores 46 

Otto-Hoffman  coke  oven 36 

Oxidizing  roasting 57 

Oxygen,  effect  on  copper 173 

"        effect  on  iron 72 

"        in  iron  blast  furnace  process 80 

F» 

PAN  process  for  washing  gold 259 

Parkes  process 227 

Parr  calorimeter 17 

Parting  gold  and  silver 270 

Patera  process 255 

Patio  process 248 

Pattinson  process 225 

Peat 24 

Pelatan-Clerici  process 269 

Penna.  R.  R.,  test  for  car  wheels 120 

Percy,  Jno.,  on  blister  steel 133 

"     on  running  out  fire 125 

"           "     on  tempers  of  steel 167 

Peters,  K.  D.,  charge  for  copper  blast  furnace 194 

"         "        on  concentration  of  matte 188-189 

Phosphorus,  effect  on  copper • 173 

effect  on  iron 72,  112 

in  alloys 289 

"             in  iron  blast  furnace  process 81 

in  open  hearth  process 153 

Physical  properties  of  the  metals 1-9 

Pig  bed 107 

"    boiling  process • 126-130 

"    iron,  manufacture  of 77-108 

"    machine 107 

Piping  in  castings no,  158 

Placers 258 

Plasticity  in  metals 2,  167 

Plating  processes 291-294 

Platinum,  metallurgy  of 280 

Plattner  process 264 

Pneumatic  process  for  refining  iron "? 137 

Pocket  ores 47 

Polling  copper 202 

"      tin 242 

Pot  steel  (See  Crucible  steel) 

Precipitation  boxes  for  gold 267 

Press  forging 164 

Producer  gas 40-45 

Puddling  furnace 126 

process       124-130 

Pulling  test 3 

Pull-over  mill 16^ 

Pulverizing  ores 51 

Pyrites 67 


INDEX  305 

Pyritic  smelting 197 

Pyrolusite 278 

Pyrometer  records  of  hot  blast 102 

Pyrometry 19-22 

Pyromorphite 209 

Pyrrhotite 67 

<? 

QUENCHING  steel 166 

Quicksilver  (See  Mercury) 

R 

RAIIy  specifications 169 

Reaction  process  for  smelting  lead 215 

Recalescence *  ' 167 

Rectangular  copper  furnace 191 

Red  fossil  ore 66 

Reduction 16 

Refining  processes 47 

"         copper 201-208 

"         gold 270 

"         iron 124-157 

"         lead 224-230 

"         mercury 244 

"         silver 257 

"         tin 241 

"         zinc 239 

Refractory  gold  ores 260 

"          materials 10-15 

Regenerative  firing  (See  Heat  regenerators) 63 

Regulus 174 

Reheating  furnaces 165 

Retort  furnaces 62,  228,  236,  252 

Retorts  for  Belgian  furnaces 235 

"      mercury 252 

Reverberatory  furnaces 62,  127,  145,  176, 184,  214,  229 

smelting,  copper 184-189 

smelting,  lead 214 

Roasting  ores 57 

"       copper  ores 174-183 

"        lead  ores 212 

u        silver  ores 247 

"        zinc  ores •  233 

Rock  breakers 5° 

Rotating  Bessemer  converters 140 

Rotary  calciners  and  roasters 178-180 

Running  out  fire 125 

Russell  process • 256 

S 

SAND it 

"    molds 116 

Scaffolds  in  iron  blast  furnaces 84 

Scale,  iron 76 

Scott  bosh  plate 88 

Scrap,  steel "6,147 

Screening  ores 53 

Self-hardening  steel      74 

Separator  for  silver  pulp 252 


306  INDEX 

Settler  for  silver  pulp 252 

Shaft  furnaces '   *  ' 6l 

Sickening  of  mercury 264 

Siderite 67 

Siemens  furnace 145 

"        -Halske  process 268 

"        -Martin  process 145 

"        pyrometer 21 

"        regenerator     63 

Silica 10 

"     brick ii 

Silicon,  addition  to  steel 149 

"      effect  on  copper 172 

"      effect  on  iron 71,  112 

"      in  copper  blast  furnace  process 198 

"      in  iron  blast  furnace  process 82 

"      in  open  hearth  process 152 

Silver,  extraction  of 246-257 

"        in  copper  smelting  process 199 

"        in  copper  refining  process 207 

"        ores 245 

"        properties  of ,   .   .    .   .  245 

Skimmer  for  pig  iron 106 

Slabbing  mill 161 

Slag 15 

"    acid  converter 143 

"    copper  smeltery 189 

"    iron  blast  furnace 83,  107 

"    lead  smeltery 222 

"    open  hearth 154 

"    puddler's 124,  129 

Slipping  of  stock  in  iron  blast  furnaces 84 

Sluices 261 

Smelting 15,  47 

"        aluminum 276 

"        chromium 279 

"        cobalt 275 

"        copper       184-199 

"       iron 77-109 

"        gold 260 

"       lead 214-223 

"        manganese 278 

"        mercury 243 

"        molybdenum ~. 280 

"       nickel .- 273 

"       silver 246 

"        tin 241 

"        vanadium 280 

"        zinc 236-238 

Smithsonite 231 

Soaking  pits 160 

Softening  lead 224 

Specifications  for  steel 168 

Specific  heat  pyrometer 20 

Specular  ore 66 

Speiss 174 


INDEX  307 

Spelter 232 

Sphalerite 231 

Spiegel-eisen 72i  279 

Spirek  furnace 243 

Squeezer  for  wrought  iron 129 

Stall  roasting i?5 

Steel 131 

"    alloys 287 

"    manufacture  of 131-169 

Stetevelt  furnace 247 

Stripping  ingots 159 

Sulphrte  process  for  extracting  copper 199 

"         process  for  extracting  silver 255 

roasting 173,  199,  255 

Sulphur,  effect  on  copper 172 

"         effect  on  iron • 71,  112 

"          in  copper  smelting    ....'••' 198 

"         in  iron  blast  furnace  process 81 

"          in  open  hearth  process 153 

"         removal  from  coke 38 

Surfusion     .   .   .    • 284 

Sweating  copper-lead  pigs 224 

"         tin  pigs 241 

T 

TABLES,  alloys 287-288 

"      calorific  power  of  elements 23 

"      charge  for  copper  blast  furnace 194 

14      charge  for  iron  blast  furnace 99 

"      charge  for  lead  blast  furnace 219. 

"      composition  of  fuels 45 

"      history  of  open  hearth  heat 154 

"      matte  concentration  in  converter 196 

"      matte  concentration  in  reverberatory 188 

"      physical  constants  of  metals 8-9 

temper  colors 167 

Talbot  process 156 

Tapping  iron  blast  furnaces 105-107 

"         open  hearth  furnaces 149 

Taylor  gas  producer 41 

Temperature  of  hot  blast 102 

Tempering  steel 166 

Tenacity  in  metals » 

Tensile  tests $ 

Testing  cast  iron 119-120 

"      coal         , 26 

"      fire-clay 12 

"      machines j 

"      steel  rails 169 

Tetrahedrite •  • 171 

Thermal  calculations  of  iron  blast  furnace  process 108 

Thermit  process 290 

Thermo-electric  pyrometer 21 

Three-high  mill 163 

Tilting  furnaces 155 

Tin,  metallurgy  of 240-242 

Tin  plating 291 


308  INDEX 

Titanium  in  iron  blast  furnace  process  ............  «  .  ;   ........  82 

"         in  iron  ores    ........................  ........  67 

Tom  for  washing  gold  ................................  260 

Toughness  in  metals  ................   .................  5 

Transverse  testing  ..................................  4 

Tungsten,  effect  on  iron  ...............................  74 

"           metallurgy  of  ...............................  279 

"           separation  from  tin  ore   .........................  241 

"           steel    .........   ..........................  74,  287 

Tuyeres,  iron  blast  furnace  ............................  89 

LJ 

UNIVERSAL  mill  ..................................  161 

\/ 

VANADIUM,  effect  on  iron    ............................  75 

"           metallurgy  of  .............   .................  280 

steel  ....  ...............................  75,  287 

Vanliew,  W.  R.,  on  Bessemerizing  copper  mattes  ..................  196 

Volatility  in  metals  .................................  6 

\A/ 

WALIy  accretions  in  iron  blast  furnaces    ......................  84 

Washing  gold  ores  ..................................  259 

"         ores    ....................................  54-56 

Washoe  process   .........   ..........................  249 

Water  gas    ......................................  44 

"       jackets  for  blast  furnaces  .........................   59,  189,  217 

Weathering  ores  ...................................  48 

Wedgewood's  pyrometer       .............................  20 

Welding  ..........................   ............    7,  289-291 

Wellman  furnace    ..................................  156 

Wetherill  separator  .................................  57 

Wet  processes  (See  Reaching)  ............................ 

White-Howell  furnace  ............................  •  .  .   .  180 

White  iron  ......................................  112 

"       metal  .....................................  174,  187 

Wild  heats  ....................................    143,  149,  158 

Willemite    ....................       .  .   ...............  231 

Wire  drawing  ...........   .........................  5 

Wolframite  .....................................  279 

Wood    ........................................  24 

Work  lead  ......................................  246 

Wrought  iron,  history  of    ..............................  121 

"      manufacture  of    ...........................  124-130 

"      properties  of  .......................  v  .....  123 

,Z 

ZIERVOGEI<  process   ...............................  255 

Zinc  dust  ...................................   ....  238,  268 

"    extraction  of  ..................................  234-239 

'    history  of  ....................................  231 

"    in  copper  blast  furnace  process    ........................  198 

in  copper  refining  process  ...........................  207 

in  cyanide  process    ...............................  267-268 

in  iron  blast  furnace  process  .........................  33 

in  lead  blast  furnace  process  ..........................  221 

in  Parkes  process  ................................  227-229 

ores  .......................................  231 

plating  .....................................  292 

properties  of  .................................  232 

refining  of    ...................................  239 


DIVERS/7 


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